I have an 18x24 portfolio which fits most prints. Assuming you've been buying your prints from the same places as me, a significant portion of your collection will be 18x24, so this would be really handy. I can't remember the brand of mine though, sorry!
I have 2 B2-sized portfolios for my B2 posters and some of my larger prints (
https://www.amazon.com/Poster-Galler...dp/B000THRINQ/). Unfortunately these only have 10 pages (20 posters) so they fill up quickly, and they're really expensive since they ship from Japan. You could probably find something better for larger prints.