I've got you on the tank knits for summer. A 1) loose fitting, 2) chunky cotton or linen yarn, in a 3) open-ish weave, is delightful for hot summer weather. The breeze goes right through it, since it's loose and off your body it doesn't trap heat, and cotton or linen don't hold funk and heat like synthetics do. Something that looks like this, or this, with a pair of linen joggers or palazzo pants, is my go to outfit for when it's too hot to think - I live in the US Southeast, so that's about 6 months out of the year.