PPS is nice, about M&P Shield size, be sure to train with that mag release though. Mags are $50 each.
Kahr PM/CM 9 is slightly smaller, long DAO but very smooth.
Sig 938 is nice but it's SAO, easy enough to shoot, about Kahr sized. Kimber Solo (if you get a good one) is similar in concept.
If money is not an issue, the Rohrbaugh R9 is a nice 9 that's just slightly larger than the LCP (no +P ammo though). Need to swap the recoil spring every 200 or so shots but if you can afford the gun, what's $5 for a spring?
Don't really have any experience with the PF-9 so can't really say but it seems solid enough.