Hey there, I can hopefully answer all 3.
Fabric- I agree Harry Hines has a lot of good places, but if you’re looking for more upholstery fabrics, Google “Fabric stores on Midway” and there’s at least 5-6 of them that are pretty good. I’ve gotten a lot of good deals in that area.
Foam- I usually get mine from JoAnne’s or Hobby Lobby with their “40% off one item” coupons and that makes it pretty reasonable.
Lumber- I’m not sure a brick and mortar is going to be very cost effective, but Rockler always has pretty good lumber, but you’re going to pay for it. Usually I shop on ebay. The lumber sellers on there seem to have best prices, and they supply a lot of good pics of what you’re going to buy. Also, they are very good about giving the correct measurements. If some of them don’t seem to have what you want, most will do custom cuts.
Good luck!