Here's a good tutorial for you: https://www.youtube.com/watch?v=CKeXQRSjk_M
When I fixed the old, rough walls in my old house, I patched the worst spots and then applied a layer of spackle, working it smooth. It takes time and a bit of patience to smooth it all, but, it can be done. If you want texture, decide if you want swirls or brush marks, or a smoother surface. Invest a little money in the tools you need, so you aren't frustrated by the process. Good luck!
Eugie: maybe this will help
Here is info to help you out
You can use textured wallpaper
You can use drywall compound to add texture
You can use spray texture in a can
How about hanging a rug on the wall
Depending on how much trim and baseboard would need to be removed and re installed. You might consider installing 1/4" drywall over it all - have it finished - primed and painted. May be less of a hassle and certainly less of a mess... Good Luck.
Hello. Could painted paneling be an option. We have it as a room lightening option in our log cabin.