Peter, I made mine out of standard 2X6 lumber. I treat them every other year and they are holding up well. A few boards have had to be replaced but that is just the nature of the crappy lumber we get here in AZ. Do not use the green lumber crap they sell in the discount chain stores. Go to a "real" lumber yard and talk to the yard guys. They'll help you find the good stuff.

Redwood is an option but I find it too soft and pricey for its worth. The manufactured stuff is indeed too hot as you mentioned. Do not use pressure treated lumber. It doesn't take stain/paint well and quite frankly, the thought of sitting on those chemicals is a little disturbing even covered with paint.

I use a stain called, "Super Deck", available at real lumberyards, and it is the best stuff I have used hands down.

Ace Hardware has a red, Ranch Red, which is also a good choice. It takes about a week to fully cure but lasts a couple of years before it needs to be repainted. The nice thing about the red is it gradually fades and the chairs still look good. You only notice the change when you replace a board or turn the chair over for that spring cleaning.

I built my chairs and swing in 1979 and I'm still using them. One tip. Use decking screws and carriage bolts instead of nails. Decking screws weren't easily available when I built them and I used nails. Since then I have probably replaced 98% of the original nails which worked loose. It also makes it easier to replace those boards which will eventually need to be replaced.