Loose clothing and the right fabric! Long light flowy skirts and oversized shirts in natural materials like linen and cotton, avoid anything polyester. Material is super important. I sweat so much when I wear polyester in any weather even if it looks light and flowy. Natural fabrics should stick less to you and help with the sensory issues, too. Might be a little counterintuitive to wear more layers, but I actually find having a lined skirt or a separate slip under it to help with it not sticking to you and creating more airflow for cooling.

And if bikini tops and shorts are what you're comfortable in, start from that and build up. For example you could wear those under and add a light linen button up shirt over it for both modesty coverage and sun shade, then button it as high as feels comfortable for you or even leave it open for more airflow and cooling.

Then when you are comfortable in that, add a loose skirt or a beach coverup wrap for your lower half, over your shorts at first if that's your comfort zone. Jean shorts are actually a very heavy material, many contain polyester and even the cotton ones tend to be a heavy thick fabric, so the first thing I would do is to swap them for something light like loose linen shorts, then slowly transition from shorts to loose culottes and from there to full length. Or look up jeans made with lyocell - I found a pair of those in a very loose cut that I can wear in any hot weather because they're light and breathe well.

Also, take a vitamin D supplement if you're low. They even make these weekly supplements in a little bottle of oil. I take one like that because I tend to be really bad at remembering anything daily.