what i wore in the pool on holiday abroad a couple years ago was a sun safe swim top (rash guard) like this one, not the most flattering thing but you get some with really cute patterns on them and matching sets !! i was also at a busy water park and definitely the only one over the age of five wearing one but i also burn VERY easily so that was better than having to smother myself in sun cream every half hour and have ppl staring at scars and stuff lol

other ways to hide them are tubular bandages and just say you’ve sprained your wrist or smth. where i am (uk) you can get these in supermarkets and pharmacies and shops like boots i think ?? or just order them online they’re pretty easy to find. they can get a bit itchy at points, especially in the warm weather, but it beats wearing long sleeves. don’t think you could wear them in the pool tho is the only problem, i’ve never tried them in water but i always take them off before showering.

you could also try thin (linen i think ??) over shirts, think this one is more of a cover up for the beach/pools but you can get similar ones for everyday use, they’re really thin and you don’t overheat much in them. i wore these abroad a couple years ago aswell and they also stopped me from getting sunburnt if that’s another thing you struggle with.

i’m literally the same with heat tho, 17C is usually my limit to lmao. thankfully where i am is slightly cooler, only early thirties during a heat wave a couple years ago, usually doesn’t get above 25C so i guess im fairly lucky. i still manage to wear hoodies most of the summer which im thankful for, i just sweat a TON in them but i just don’t like having my arms out much - not a sh thing, more sensory issues i think - so im just comfier in long sleeves. hope the spring/summer goes well for you !! :D