There is no such plant that requires little watering and little mowing and gives you a functional lawn. Cynodon (Bermudagrass) is a warm season grass and is used in the south for lawns and on golf courses. In Oregon, it goes dormant in the fall and turns brown in color. It greens up again in late spring. Once it is planted, it is almost impossible to eradicate if you want to get rid of it. Warm season grasses can get by with less water than cool season grasses. In the south, Bermudagrass is often over seeded with perennial ryegrass in the fall to maintain the green color throughout the winter. Then the perennial ryegrass dies from the heat. In Oregon, the perennial ryegrass would not die quickly and the blend of the two would not look good.
I don't know anything about Roemer's fescue other than it is related to other fine fescue species such as creeping red fescue, chewings fescue, and hard fescue, which would serve a similar purpose and are widely available. You would have to search for grass seed companies in Oregon and call them as Roemer's fescue is a specialized species with a very limited market. You might try Protime Lawn Seed (https://ptlawnseed.com/
) as they have some Ecolawn mixes that might suit you.
In general, when you don't mow grass, it thins out and other weeds and grasses invade. You end up with a mix of everything that doesn't usually look good. Golf courses often will "naturalize" out of play areas and plant fine fescue. It grows fairly tall (they don't mow it or water it), looks pretty (like a meadow) during the summer, but it thins out and gets a lot of weeds. As a result, once a year, they flail mow it in the late fall, spray the weeds, and they let it grow back in the winter, spring, and summer and then repeat the cycle.
You will have to submit your perennial question separately as I am a turf expert not a perennial plant expert.
I hope this helps. Good luck.