The determining factor would be the boat in question, and how much room you use now/wish for.
The main thing is, and I'm single okay?!?, I believe both partners need a place to go out of sight of the other for privacy. If one of you is on the fly bridge, or aft deck, or forward cabin, it helps. There will be times when you may find yourself:
#1) Planning a romantic interlude
#2) Contemplating murder or mutiny
#3) Working on a craft or boat project
Having a separate space is in my view critical for overall happiness.
And I'm perfectly pleased aboard my 23'er. To me 34 is extravagant. And doable with caveats. Specifically privacy.
Ashore when you're ticked at each other you can get away. A walk in the park, a trip to the grocery store or out to eat. Aboard a boat you'll be in tight quarter. You will rely on each other as most couples never have had to do.
For some it is an adventure, filled with joy and happiness. Others find it a short trip through purgatory with divorce or boat sale at the other end.
It's up to you which experience you end up with. Know this though, if either of you don't like the boat, DO NOT BUY IT. Nobody has an epiphany after living aboard the "wrong" boat.
Additionally, what is right for me, galley up, may well be the antithesis for you and your bride. There are a variety of boats and one will suit you.
Good luck and happy cruising.