I have similar measurements and the heavy Gildan's fit me perfectly (they're 3-5 eurodollars), in a medium. I also have a bunch of H&M shirts that I got for 1 euro that fit like a glove, but they're XL.

My suggestion is to order a bunch of different stuff, in both relevant sizes (M and L) and be ready to return until you find what you want.

15 isn't much though, and if you find something for 20 for example, even if you need 10 t-shirts it's not a huge expense compared to buying 10 shirts at 7.