You look terrific and modest.  I would suggest of you want to keep this level of coverage (which, btw, you are young and beautiful, dress for your level of comfort), sweating in cotton is not going to be very comfortable, you will be happier in a technical fabric designed to wick moisture away from your body.  Cotton will get wet and stay wet.

That said, a lot of technical stuff is very form fitting so sometimes I like to do a close fitting under layer and then a cotton tee over top (for sun blocking in the summer).

Be emotionally and physically comfortable!

You look like you have the perfect body.  It works? You are blessed.

And my big test for working out (I like to climb and do yoga) is to bend over and look at my but in the mirror.  And then shine a flashlight at my pants.  If my pants haven’t gone sheer from the stretching and I can’t see an unfortunate amount of self, then I’m content.

Love from an almost fifty, almost completely healthy female who fretted too much about her body when she was your age.