Regular lawn grass type seeds are not going to work for you unless you have no issues with allowing them to go dormant in summer as they prefer. They will still require mowing, particularly in the spring and fall when PNW lawns receive all that rainfall and grow rampantly, but will require minimal mowing for several months if allowed to go summer dormant.

There are some other alternatives - low growing groundcovers (not readily available by seed but certainly by plug or grower's flat). Ecoturf or ecolawn - a blend of low growing turf grasses and drought tolerant broadleaf perennial seeds for a no-mow, low water meadow-like lawn. Not sure how well that would figure with the turfstone. Or.....skip the turfstone and whatever filler and go with artificial turf. This is the ultimate eco-friendly and low maintenance solution. Completely pet friendly (easy clean up), will go anywhere (even lawn unfriendly situations like heavy shade or slopes), only needs to get hosed off occasionally. And the current generation of artificial turf is an extremely realistic looking product but does represent a bit of an initial investment.

If you go with an artificial turf, one little thing that needs to be done is the dog urine needs to be washed down through it. Otherwise it will smell like a bathroom as well as collecting dust (dried urine is sticky).

Turfstone makes a good driveway, but if you are going to have people walking on it, that can surprise you. High heels, in particular, will sink into the dirt/grass areas between the paver part of the turfstone. It can making walking very uncomfortable. Turfstone also collects solar energy on sunny days and releases that heat all night long. What this means is the soil becomes dry very quickly. If you were planning to water once a week, you might have to water much more frequently.

You know things are slow when you start answering questions from 2014 haha :-)