Depends on what you call nice seats. That could open up a big can of worms on here.
If you are talking about PE then that will probably cost you quite a bit of money to upgrade.
With regards to economy seats the majority of OK as far as it goes. Bulk head seem to be some peoples choice but have their limitations re near toilet, near galley and are slightly smaller than the rest
Personally if you have the money upgrade to PE, quieter in the bubble, bigger seats, more leg room and the service is a bit more personal
I know Virgin are now selling a few seats with extra leg room but these are only available at checkin.
Good luck with whatever you do and best wishes for the future for both of you
And enjoy the holiday