That's really an impossible question to answer. Airlines have unanticipated sales. Soft demand can lead to discounts. Jet fuel prices can change.
I would pick your most desired flights on Google Flights and set a fare alert, so if there is a flight sale, you can jump on it.
I prefer direct flights too. I would love to get the direct Delta flight from PDX to LHR if I were going to London.
If you book right now for next July, the Delta direct flight from PDX is just over $800 per person round trip, give or take. Not much cheaper with a connection.
British Airways from Seattle is much cheaper - $516 round trip to London for next July.
SFO might be a tad cheaper for a direct flight depending on the day but I'm guessing Seattle is much more practical for you.
I would never book something so far in advance myself, but I know some people do. Personal preference, up to you. That $516 price would be pretty tempting. I'll bet it won't go down much, but you never know. More likely to go up the longer you wait.