I've been on hormones for over a year now and my ribcage has increased in size, not the actual ribs but you know what I mean. Anywhos My ribcage below my moobs is 42in and above my moobs is 43in and my moobs is 44in. My breast tissue is really squishy and goes flat with a little pressure.

I don't have big moobs but it would be nice to just wear a t-shirt for once instead of 3 layers of clothing. What size should I get?...that will allow me to breathe comfortably, doesn't roll, and has large arm holes.

The way you're encouraged to measure is to disrobe, measure around you at the largest part of your moobs, then measure around you just beneath the moobs.  Add those measurements together and divide by 2.  That is your measurement to determine binder size.