I do all my texture work with PaintTool SAI. I love torturing myself. Genuinely though, it's all I know how to use, and I make a pretty penny doing texture work for avis, so it's really whatever works for you. I'm familiar enough with basic UV map layouts and where everything needs to go, that I just do it that way.
My point is, you don't need expensive art programs to work on textures if you're determined enough. I see a lot of people say that substance painter is a requirement, but it's really not. Just more convenient.
PNG Tree is my best friend too! For transparent textures to layer on top of things.
