I was given a Cuddle Ewe wool mattress topper a number of years ago, and I've loved it. It transforms an underperforming mattress into something lovely, cool and soft on top only, so there's still lots of support. The wool topper actually supports your body with its resiliency and has many advantages that modern mattresses have lost. This is a really nice upgrade. Two more are below.
I slept on one of these in a hotel once and slept like a baby. Bought one and slept on it for years. Totally awesome and much softer and less supportive than wool. Very much a super cozy luxury that's particularly nice in the winter.
If you want affordable luxury, is where I started my journey, and I'd still swear that if you do nothing else, cover your mattress with a nice, affordable topper like this which will give you a much softer sleep and a better night of ZZ's. Most good affordable pads are poly filled, but will come with really nice cotton fabric out shell, which makes a difference, like this one.