ExOfficio Women's BugsAway Lumen Full Zip Hoody
ExOfficio makes mesh shirts with insect/mosquito repellant (so that you don't have to keep reapplying bug spray). They have long sleeves with thumb holes that cover the tops of your hands and they (crucially) extend down in the back to cover your lower back/upper-butt when you crouch down/lean over, but the mesh makes it tolerable even in very warm weather. It’s the most expensive shirt I own and it’s 100% worth it.
Update: it seems like they’ve discontinued this particular shirt (which makes no sense). There are similar things out there, like this full-zip hoodie from Insect Shield, or this hoodie from L.L. Bean, or maybe this jacket. But I really loved the way that the mesh one from ExOfficio was basically a super-light jacket you could put on over whatever else you were wearing, even/especially in the heat of the summer.
So you might also consider hunting for something really versatile and then treating it yourself with permethrin, which I usually see recommended more forTick bite avoidance & tick removal.
(Not sure where to put this, but mosquitos aren’t very good fliers, so if you’re in mosquito country, try to plan excursions when it’s breezy out, and if you’re on the porch, bring out a fan and set it to oscillate around the area where folks are seated.)
If you do end up with bites, try treating them with a Mosquito bite relief: a tiny heater.