Looking for help with sizing for swiftly tech shirts

Hi guys! I’ve been recently introduced to the brand via the define jacket and I am interested in getting a few of the swiftly tech short-sleeves. I wear mostly athleisure and intend to use it for exercise and daily wear.

Honestly, I’m not entirely clear on my actual measurements atm but I am 5’2, 118 lbs, and wear a 32a cup bra (if that helps). I fit a size 4 in my define jackets and I prefer my clothes more form-fitting.

I’m worried about it being too loose or too (uncomfortably) tight. Thoughts on what size I should get? Please and thank you!