i’ve really come around to diceless skills (not thief-specific, i mostly play Knave hacks instead of retroclones, but you probably could finagle it into a thief in a more traditional D&D game).
the idea is each character starts with X number of skills (more for a thief), and instead of picking from a list you just write something you’re good at. picking pockets, or sneaking, or alchemy, or smuggling, or swimming, or whatever. and any time that comes up in play, unless you’re asking for something genuinely unreasonable, it just… happens. you do it. you’re the climbing guy, you can climb shit any time something needs to be climbed, end of story.
i like skills being more reliable, since i feel it’s in the OSR spirit for dice to be dangerous. combat has lots of die rolls that can kill you, on purpose, as a deterrent to keep you from approaching every situation with swords drawn. that way you end up finagling a complex scheme that requires no dice, which is usually more interesting than murdering people to death. diceless skills in that context end up being another tool for you to integrate into your schemes, like your crowbar or rope or big pile of gold, instead of another way to leave your character’s fate up to chance (which should always be opt-in as a way for players to make interesting decisions about risk management).