Agree with your take on the #6 being our problem position. Wharton is probably the most natural fit and I have very high hopes for him, but he's still a little raw and needs to make a move to a club who play a more possession style of play to be sure he can hack the responsibility in possession at international level. He's also been injures for ages.
Mainoo simply isn't a #6 for me. Too poor defensively, and not positionally responsible enough.
Gomes is nice and tidy on the ball and is sort of the right profile if you're looking for a playmaker mould, but he can't play there on his own, at least not against any half-decent opposition. He's tiny and would get absolutely bullied, and offer nothing in defence. Maybe he could be paired with a Rice or Gallagher in a double pivot, but that means you have to sacrifice one of the #8s going forward, and ideally we want to fit both Bellingham and Palmer into the midfield. (Although if it simply doesn't work I'm open to dropping one and simply playing a double pivot. Midfield balance takes precedence over personnel).
Another option: been analysing the City Madrid game and I think Stones did the job very well in that first half. He's not particularly progressive on the ball but he doesn't lose it, you can pass to him in tight spaces and he keeps it extremely well. And of course he's good defensively. Looks to me a better fit for the solo #6 role than Rice does at least. Something to consider.
Obviously we'd miss him in the back line. But Guehi is a very talented CB and is a captain for his club. He could potentially lead the back line adequately in Stones' absence.
Then there are plenty of talented options for who could play next to him. Colwill, Branthwaite, Konsa, Ben White if Tuchel gets him back into the fold.
Not saying it would definitely work but could be an option worth considering.