Keep an eye out at thrift shops, maybe? I assume those exist near you. Probably much less availability that way, so you might have to look for a while, and fewer pattern options as a result, but cheaper and for a test maybe better because already pre-softened through wash and wear?

Bamboo? I have bamboo socks that are warm and soft, but they take a little extra to dry

Yeah, wool is good in hot weather as well. Especially since it very effectively combats body odor. I was just trying to give a rule of thumb.

Yeah, logistics are hard & I imagine a small bar/café doesn't have the (kind of?) staff to think about straws or where else to search for the ones that don't fill costumes with nasty shit - they just pick whatever their usual supplier has on offer so it's less paperwork.

And it's not like anyone blamed them for shitty straws anyway.

Cotton feels sweaty all the time

The opposite for me, synthetic clothing makes me sweat like a bastard, I try to only buy 100% cotton shirts and stuff

Get yourself a merino wool base layer shirt, like a thin one not sweater thick. It'll be surprisingly cool.

Try hemp or bamboo fibre (has different names like rayon, tencel, lyocell).

You could try different thicknesses of cotton and see how it feels. Or cotton blended with the other materials. Some companies list their shirts as lightweight or heavyweight or give cloth weight in gsm (grams per square meter) or oz (ounces per square yard). A lightweight and oversized shirt will be good in the heat.

I live in Australia and I wear 100% cotton very regularly, including summer. It was 39° today and I've been wearing a cotton shirt all day.

It certainly does not feel sweaty all the time.