Just throwing it out there...I use Skyscanner generally to look for flights and serafina 's suggestion is good too of course.
These days even the "premium" airlines charge extra for seat selection and baggage and it's something I struggle to get used to and accept. I don't mind on Easyjet or Fly Bondi or similar as that was always the way but it just feels wrong otherwise with big airlines on long flights.
I generally travel alone and like an aisle seat so I can get out of my seat nice and easy. I don't mind at all about people disturbing me to get out to the toilet or whatever as I don't sleep in economy anyway.
When I returned home in May on Iberia I didn't book and pay for a selected seat in economy as I was considering buying a last minute upgrade if it was offered to me. Anyway that didn't materialise and I ended up with a window seat. I guess it could have been worse and ended up in a middle seat.
Keep us updated Splinter as to what you come up with.