Ok a few things to think about and one was touched on. Parasites. If you live in an area that only gets lows into the 50, you are going to be fighting a major load of parasites all year round. Not to mention insects. Freezing helps kill off insects. Random bouts of freeze and warm kill them off even better. Also, with 50 or even 40s for lows and no desert, you are most likely looking at nasty high humidity in the warmer months. Not to mention the higher in elevation you go the colder winters you will get. So you will wanna be low landers. Low landers with enough rain to keep stuff green... tropics and crazy amount of rain. So you see, what you want, you dont really want.
I live in S.E. Washington state. Where I am at, its kinda a desert but I can go about 80-100 miles in any direction and be into mountains, fun, fishing and hunting. Summer temps can get pretty high. This year we had the most days over 95 degrees on record for this area but the year before, just 1 day over 100. Winters are mild with usually just Dec. and Jan. getting a good chilly bite to em. Winter lows kinda mirror summer highs in terms of total days. Maybe get 2 weeks sub zero temps day and night but most of the time above freezing during the day. Snow fall is minimal most years at a few inches that usually melt the same day but not unheard of to get a nice wet winter with 4-12 inches at a go. Annual rain fall average, 10 inches. Summer humidity is low cause of the arid climate at a average of 25-30%
We are currently having above normal temps. Right now at 10pm, Nov. 10th, its 43 degrees. Low expected to be 38. High of mid 50s. So over all not a bad place. Would guess going a little more south into lower Oregon or upper California would be better. But here is a major factor. If there is such a place as you have your mind set on, its already occupied and its EXPENSIVE as hell

Good luck