If you bought the K10D new, you've had it a long time. A fine, ground-breaking Pentax at that time, and still a good camera. But it has been long surpassed in most every respect. That said, you are used to a very durably-built body with a pro-style control set. There are also advantages and disadvantages to every design concept now out there. When getting too small, ergonomics can become totally unsatisfactory, along with minimal controls and less conveniences for making fast adjustments, perhaps even no built-in flash for a grab shot or fill.
The KP's design concept was for very well-built metal construction (magnesium alloy) but in a more compact design to offer the larger APS-C sensor in a DSLR, to be competitive with APS-C size mirrorless. This addresses the need of those wanting the compact advantage of mirrorless, but with APS-C and an optical VF, and also a unique control set up to pro standards. In addition, its concept included the seemingly impossible goal of image quality, including lower noise, that is as near the full-frame K-1 as possible. All tests have indicated these goals have been successfully reached in the KP! I have liked mine so much I bought a second body!
My recommendation is- go the extra yard for a KP and the DA 18-135mm DC WR lens. Coming from the lenses you now have, you will love the DA 18-135mm DC WR, I am sure. AF is very fast, quiet, and accurate. IQ is good to excellent, with central image area at the excellent level throughout its great zoom range. It is very compact for the zoom range, well-built, and good-handling. The KP will offer the high build quality you are used to in a more compact form, with a lot of performance improvements.
Last edited by mikesbike; 06-02-2018 at 10:08 AM.