You could try to get a hand-me down quality mattress on the cheap or even for free on craigslist? People who move out of town after a year often leave mattresses as good as as new... It wouldn't be much different than sleeping on a hotel mattress.

Have you looked into getting a organic latex or wool topper? There are bed cooling products out there, here is a website that sells products to combat the Tempurpedic mattress warming issues.

http://www.drinights.com/store/merchant.mvc?Screen=CTGY&Category_Code=sleep

I would not buy a used mattress because of the bed bug issue.

I have Grave's disease as well and just purchased the Terpurpedic Cloud Supreme. I have cotton sheets and this cooling mattress pad. http://www.sleephappens.com/html/buy_online/product_detail.cfm?productID=1399 So far I've loved it.

I also have a memory foam mattress, and I have similar problems with it. I always have a mattress pad that is all cotton, which can be a little harder to find, but synthetics will not help wick away moisture and keep you cool. I also only use 100% cotton sheets and blankets. I have considered a wool topper like the one b77 suggested, and I do think that is the best solution. The one caveat is that the mattress pad does affect the way weight is distributed across the mattress. If you are a back sleeper, this probably won't mattter at all, but as a side sleeper, I do find myself in a hole sometimes. Good luck and sweet dreams!

If you haven't found a solution yet, what has worked for me is an egg-crate foam pad on top of the memory foam, lumpy side up. This helps with creating air pockets. I just put a regular mattress pad over that. Good luck!

I have also had this problem! We have a foam mattress topper that heats up like a sauna. Our solution was to put a quilt/blanket directly on top of the foam and then cover with a mattress pad. Adding the pad on top helps secure the quilt so it doesn't move around. We sometimes take the quilt off in the winter-time to keep us warmer at night--which allows us to turn our heat down and save money on our electric bill!

Open your window at night and turn off your heat.
Would a fan by your bed help as well, along with some of the other above suggestions?

This pad sounds like it could work.

http://tinyurl.com/4nq8svk

It's not cheap but it's cheaper than a new mattress.

I want to get some of these for our beds in the summer time!

I would recommend finding a gel foam topper for your mattress. Again, they're not cheap, but I'm sure that they'll cost you a lot less than a new mattress and the cost-benefit will be well worth it.

Some other adjustments that may also help you out:

- Get a programmable thermostat. You can set it to progressively cool down through the night so that it's chilliest in your home when you would typically wake up hot. 60-68 degrees is the optimal range for sleeping.

- The "facts" about how much body heat you lose through your head have been discredited, but your face and head are more sensitive to temperature changes, so aim a fan at your head. I sleep like this year-round, so when I sleep somewhere there's no fan, I almost always wake up hot.

- Get a pillow that absorbs your excess heat.

Consider investing $80 in a Bed Fan - a fan that blows air under the covers. It doesn't work well for restless sleepers who untuck the covers, but satisfies many others.

http://www.amazon.com/TOMPKINS-RESEARCH-INC-Bed-Fan/dp/B001Z0OZGE

SNUG FLEECE wool mattress pad. Wool breathes really well and I love mine.

I also have Graves Disease. It's a b***h in the summer, because I love to sleep with my windows open. The best way I've found to combat waking up at 4 am drenched in sweat is thin layered blankets on top, and a quilt made of cotton (VERY IMPORTANT that it's cotton and not some other fabric) underneath my fitted sheet but on top of my memory foam mattress pad. The mattress pad is going to be warmer than not having it. Also, having a fan aimed at your head really does help. Wool and Fleece really don't help to cool me off, eventually they get warm too.

I've been living with this for almost a decade and I've always got a fan going at night, summer or winter. Good luck!

I have a box fan and have it blowing under the bed. The air seems to come up through the mattress and keeps it cooler.

I use a Coolmax mattress pad during the summer and its helped keep me from getting overheated. Sometimes I use a Coolmax pillow when its really warm, also.

Oddly enough, I use a feather bed in the summer over the Tempurpedic. Helps regulate my body temperature better. Also, sleeping naked helps. I'm always over heating if I wear pjs.

You could try finding something similar to either of these products: http://www.coolgelmat.com.au/original
or
http://www.innovations.com.au/Product_Detail.aspx?ParentCategoryID=165&CategoryID=220&ProductID=86610

I've just bought two of the innovations ones - one for hubby and one for our little girl. It won't stop you from heating up, but it will stop the bed underneath you from heating up, and thus, stop making you get hotter.

I would see the problem with heat dissipating, It would help if you use thin sized mattress and keep the room cooler.

Memory Foam Mattress Reviews

I can relate to the issue of hot memory foam. I started using Cool-jams pajamas and temperature regulating bedding which has helped tremendously. The pjs wick moisture and the sheets and mattress pad keep the entire bed cool. Great products that I found online.

I've been having this same problem this summer... the other night I dragged my poor boyfriend out of bed at 2am just so I could yank the memory foam topper off in sweaty frustration. Can't really afford a new mattress right now (though when the time comes, I hear natural latex is the way to go?) but will definitely try putting something over top of the memory foam!