Hi, we got Rentokil in who were brilliant. I know it’s expensive but there is never just one mouse, (unless, like my DSis, you see the cat bringing one in🙀) The longer you leave it, the harder it is to get rid, ime. And, also from experience, it’s almost impossible to get rid of them yourself. Rentokil know the best place to put the traps - the person we called in put them in the most hard to reach places, but it worked.
Rentokil guy also told me - don’t know if it’s true, but it’s a great thought - that mice travel in advance scouting parties when moving in somewhere. He said he expected to find at least seven, even though we’d only seen one. In the end, he caught nine, I think.
They ask how many rooms so they know how many traps to lay/quote for - they need to put traps in every room.
Ours were dead and gone very quickly.
Good luck with whatever you decide.