You probably don’t need to be told about sleep studies indicating that bedfellows affect each other’s sleep. Getting the largest bed you can handle is recommended, as well as limiting springiness/movement transfer.
But through further experimentation, I’ve discovered that having a king size total area but with a full sized sleeping area (in my case designated with a mattress topper), gives a welcome buffer on each side of the bed and stops me from worrying about how close I am to the edge. It’s hard to say whether it’s better for everyone, but it’s been good enough for me to recommend trying it if you have the opportunity. I’m also generally in favor of more innovation/experimentation in this area. (I literally take my best naps when in a tent and I have friends with “sleep pods” who love the coziness (while I know other people who have their bed in a big room with a wall of windows facing the woods).)
The image above is the "Defalco Platform Bed" from Foundry Select — it's seems to be a commercial version aimed at the upgrade. The poor man’s version is maybe just testing out having your mattress directly on the floor.
(I thought this was a cool anecdotal study — the data on “shared bed with partner” was interesting and ~tragic)