season (Fall, Winter), they all start trying to sneak in, make their way into my home. I have 3 dogs and although sometimes they're good mousers, it's not enough.
So, usually in the early fall, I put glue traps out and do so knowing that yeah, sure maybe one of the dogs will accidently get caught in a glue trap, but they are big enough so it doesn't overwhelm them, and they can manage until they get my attention (to pull the offending glue trap off their paw). They are smart enough to avoid the glue traps for 99.9% of the time, but sometimes they mis-stepped and OPPS, they're caught. Easy enough to pull the trap off since they are designed for spiders and insects, small mice.
Then, in the Spring, when the mice disappear (I guess if any are left, they go back outside), I pick up the glue traps, so they won't be in the way when I do my normal clean the floors routine, etc. In these cases, I also don't just throw the glue traps away, I move to a basement (unfinished) or garage, so they'll continue to be effective. I don't have any little critters in STLMO (lizards and such, I don't want to kill them), so I don't have to worry about accidently getting the wrong sort of critter on the glue traps.
By the way, cats are the best policy against mice, so you're doing good there. As to being in your walls? Well, all I can say is that they do get hungry and thirsty, and do come out to find something to eat and/or drink. I suspect that a professional mouser would claim that they would have to 'bomb' the entire house, to be totally effective in getting rid of the mice in the walls. I would do the above first (glue traps etc.) prior to going this drastic route, as you and your pets would have to temporarily relocate.
Good luck!