Love the idea of painting fabric. Helloooo - Textile Designer!! Painted your own fabric would be step one! If you can't screenprint (which you totally can do at home too) painting would be great.
Polka dots that are wispy would be great and easy to do with a wide and bristly brush and no care about the exact pattern - or could do a quick half drop.
Beware of too many stripes in one room. Make sure they become either all the same (maybe) or have a lot of diversity so they dont visually compete.
The bold stripes on Pintrest are great, a large stripe that could mix with the smaller stripes of the room, but yes STIFF, especially depending on the paint you use. If you are going to do wide stripes - just sew them. Its still super easy and you don't have to concern yourself with the large panel to have to paint on. Large panels could end up becoming costly or have to be pieced together, and then your stuck with a seam.
In Conclusion - sew wide stripes.