This is a difficult one. Obviously, the fabric you wear makes a big difference; natural fabrics don't make you sweat quite so much as artificial fibers, but cotton, for example, is not the most practical of summer fabrics. Cotton wrinkles up in your suitcase and needs to be ironed. Who wants to do that when they are already too hot? Fabrics like cotton have no stretch, and that's another reason cotton garments are not always as comfortable as their artificial equivalents.
For short heavy ladies, the problem is often that we tend to 'glow' a lot. Let's not pretend. We sweat. We turn red. It's all rather unpleasant. I often suffer from heat rash if I'm not careful, so what's my solution?
As always, I dress in layers and loose clothing; I like to stay comfortable. If you don't like exposing your arms, a loose kimono type jacket is ideal, especially in a very light fabric like printed polyester chiffon. (Try Torrid.com, for example) Otherwise look for a wide chiffon shawl or ruana; even a pashmina is ideal for summer. If you suffer from chafing, you may find trousers (pants) more friendly than skirts and check to see if your deodorant is just a deodorant or also an antiperspirant. I find spray body oil indispensable in the warm months (as long as it's non-greasy) as it helps to stop heat rash (I get mine from Etsy in some fabulous fragrances), and I spray it on all over before getting dressed. If you suffer from heat rash, you might like to get a good thick body lotion and add some lavender oil which is great for removing inflammation. I stick to basics, trousers or pants with a T-shirt (try daily rituals on Amazon) in the same color as they can make me look as tall as I can be (I'm only 5' or 1.5m). I add this to something more colorful but thin (pashmina/wrap/ruana/kimono) thrown over the top. On holiday I might wear a long dress in the evening, put more/some makeup on and add some jewelry, but that's about it. If I'm honest, I avoid all those 'cool' fabrics we're told to wear in summer because I hate looking creased and I don't intend to spend my vacation ironing.