As for what to wear, you can go to a sportswear store ... a sportswear or sweater is fine ... long sleeves are of course ... You said that your gym has no air conditioning ... It would be better to wear long sleeves ... At least you won't catch a cold easily after sweating ... Just wear one ... After all, if you want to exercise ... after running for a while, you will sweat all over ... You will regret wearing too thick clothes ... Sweating ~! Wait, wait, wait. Ask the clerk. She can give you good advice ~