Best way to shrink jeans that are a bit too loose?

Inspired by the too tight thread as I’m having the opposite problem. I’m smack between two sizes and my jeans are all too loose to look good, but I think the next size down would be too tight, and I’d rather not buy new jeans if I can help it.

So far, I’ve tried washing in hot water and drying in high heat, but not much luck with that holding for long as they get saggy fairly quick after wearing for about an hour.