I totally understand you, I am petrified of snails (and fyling insects, jeez, it sound so bizzare as I'm writing it down xD)! I would take a spider over a snail, tbh. I had a brown algae bloom in my tank tho a few weeks ago and I felt like my betta could profit from a tank mate, so I bit the bullet and got a nerite snail. I've had him for nearly 2 weeks in my 7gal. He hasn't crawled out yet or anything (I do get paranoid when I can't see him tho or anytime he climbs up a bit higher xD), but I covered all I could to prevent him from it. I got a freakishly fast one as well! :O I've never seen a fastest snail in my life (so I named him Bolt for that matter xD). Great at cleaning algae, he does produce quite some waste, but it's not as bad (again, I have a 7gal NPT tho), let alone impossible to clean. So far so good, I guess you could say.
I guess shrimp are less likely to crawl out? But I have zero experience with shrimp, so I shouldn't talk about it, really.xD