Just recently did this. The space in between didn't really bother us and it's so much nicer for motion isolation and being able to customize your adjustment. It's funny how big a twin xl feels when it's next to another one. More on reddit.com

I bought one a few months ago and I really like it. I have sleep apnea and back problems- I feel more rested. It’s for back sleeping mostly But you can still set it so it’s flat like a regular bed or slightly raised which I try occasionally while lying on my side Mine has a remote with a Anti-snore button that raises your head/chest to good angle in few seconds It also has two massage motors - but I find them a little weak - (gimmicky ) like from a 70s hotel - put in a quarter and the bed jiggles (cue Barry White smoke machine and mood lighting) I bought mine off Amazon as the selection was bigger than the stores- some charge a lot more in the store. The adjusting frame can sits inside a regular bed frame- you would remove the cross brackets. Split king bed could be done with two twin XL beds side by side- so your partner can have different adjustments More on reddit.com

Nectar has the the best split king adjustable base by far! We preset positions and it's everything you might need, massage included 😁 I believe we bought it with affirm and I was sorry at the time but never looked back. More on reddit.com

I keep looking at them, but then wonder if it wouldn't be irritating to be stuck having only the positions the adjustable frame adjusts to. I'm dithering about whether or not I shouldn't just keep using a foam bed wedge for my head/shoulders and foam feet wedge (forget what it's called) on my box springs so that I can move them around to wherever I want on any given night or nap. I'd like to hear from people who currently use adjustable bed frames about whether or not they get aggravated at only having the various positions that are built into that frame, or if those positions are always what you need? More on reddit.com