Good for you!! (me too..bustin' out to bright and happy colors!)..I will now let all the incredible AT readers give you wonderful and awe inspiring ideas..they always do..can't wait to see!

I think you would be fine with stripes, wide and/or thin, and a smaller scale modern pattern of just about anything. That bedding is really fairly nuetral I think both in color and organic pattern.

oh and i love the idea of orange and plum with some black!

I don't have any specific suggestions, though I have two concepts to consider:

1) I had a coworker who has a crazy eclectic house. She said everyone who comes over asks her how she chooses things to work with what she already has. Her answer is that she doesn't -- she picks individual pieces she loves, and since she loves everything else in her house, it all sort of works together. You could try that, but always bring a pillowcase with you when you shop so you can see what they might look like together. I think if you find one or two fabrics, you're set. Also look at fabric places online. Even if you can't afford a fabric, you'll get a better idea of what you are looking for.

2) Maybe go through Ikea's website. They have a knack for combining bright colors and fabrics together.

3) Okay, maybe I have a couple of suggestions: try Amy Butler fabrics. They're cheery and run the gamut from saturated / desaturated, in tons of colors. Also, check out the Marimekko website for other fabrics. Maybe fabrics from the same company might work well with it. Lastly, maybe stick to an organic theme: Leaves, branches, etc. Sometimes giving yourself restrictions helps to focus your search.

Good luck! I love the comforter!

"Is there some way to incorporate other prints into the plan to add color or did I bold pattern myself out of options? What should I look for? Are there any good online resources that aren't too expensive ?"

Especially if your room is small, I suggest limiting any other fabric prints to your sheets and keep your window treatments and upholstery in a solid color. However, if you have some space, I'd consider a black and white print with the Merimekko duvet you chose. For example, a large scale branch/tree print on an arm chair with a violet or magenta pillow.

An area rug is another potential spot for a coordinating print. I would go with tone-on-tone so that you're not arguing with the duvet. Mabye try a grey on charcoal combo, or lavendar with plum, or yellow with godenrod, etc. It will read as a solid color, but still have have the texture and fun of a print.

As for fabric resources, there are a TON online.
search "discount upholstery fabric" and make sure you have lots of time to peruse the pages. Order samples before committing to your purchase.

I would look for plaids, stripes, and small scale grid patterns that have at least one of the colors in your existing bedding.

They sell coordinating shower curtains in that same fabric at C&B. Could either be cool or overkill though.

Before you attempt mixing in more stuff, maybe you should work on getting what you have now in order. An iron would be nice, for starters, on that wrinkled comforter. The art in the background is hung way too low and you say your walls are tan, but they look purple in the photo? Being clean and simple in design is sometimes better than overkill with patterns, especially if you are not good at it.

Hey! That is my room, my bedding and my cat but I didn't write that letter! That is why the wall color doesn't match up with the one in the letter.

And the artwork is hung too low because we had just switched rooms when I shot this photo of the bedding and has since been taken down. And as for ironing I never thought my photo would be published if I had I would have broken out the iron.

I think the easiest way to bring more color into your room would be to mostly use solids. I'd limit them to maybe 2 or 3 choices, and repeat each of them in at least three spots, even if it's just a small detail somewhere.

Your print is three colors: black, white, and a certain shade of green. Your print is also very linear and stylized and fairly large scale. If you look for other linear, stylized prints that include at least one or two of those colors plus another single clear color (black/white/ ?, green/white/ ?, etc...), they will probably work together, especially if the proportions of color are similar to your starter print -- as someone said, take a pillow case along to view together, and if it doesn't look right, skip it. (Prints with a lot of white in the background might be easier to blend.)

Another option is more of all three colors in different designs and proportions. (Say narrow stripes of green, white, black, and maybe one other color -- maybe gold, or something resembling the tan of your walls, to tie them into the design.)

Another choice might be plain colors, like plain plum. (If you do that, I'd suggest a fabric that isn't a lot more formal than the cotton of your duvet, but maybe something with a little sheen, like a polished cotton or MAYBE dupioni silk. (I'm imagining pillows, here, by the way.) (NOT something of a radically different texture like velvet or brocade.)

I'd avoid small prints, I'd try to get some tan like your walls and carpet into the mix, I'd keep the additional colors mainly in the same value range as the green (clear, slightly muted with white, not extreme in either brightness and saturation nor in darkness -- if you do use plum, I'd choose any other colors lighter.)

Obviously plain black, white, green and tan are already options that will work fine.

Good luck!

I found this helpful to mix patterns - it's a very short "how to" guide with pictures:

http://reviews.ebay.com/Decorating-with-Fabric-Mixing-Fabrics-and-Patterns_W0QQugidZ10000000000734125