If the girl is right (?), then do whatever is necessary to make her happy on board. I repeat: whatever is necessary.
Because if she's not happy, then you won't be happy, either, period, so having the boat the way you like it will be utterly wasted. In fact having any boat at all will be utterly wasted.
If it's just a question of space, then you don't necessarily need to go MB or cat. Monos of similar interior
volume and quality cost about the same as cats -- they are just much longer. And the bonus with a larger mono is that you have proportionately better load carrying capacity -- which is kind of good thing to go with the interior
volume. Big monos (I sail a 54' Moody) are comfortable, spacious, carry loads well, are faster, more stable, more seaworthy
, have a more comfortable motion, etc., etc. -- many virtues. And are not hard to handle with powered winches and windlasses, etc.
You might look at cats for a different reason -- many females hate heeling. Besides that, cats have a better feeling of space and view from the salon
than most monos (some monos, however, with raised saloons, are not so bad). I'm not a cat man myself, but I would go cat in a heartbeat if it were necessary for the kind of reason you are facing.
If you like to sail, I don't know why you would look at mobo's. You will lose sailing -- and many otherwise finicky females like sailing, at least in good weather
-- but that's not the only disadvantage -- mobos have minimal or no keels or ballast, and have a much less comfortable motion both underway and at anchor
. It is a little known fact, but this is the real reason why most "cruising" mobos spend 99% of their time in a dock
or marina slip. This is a problem which will not win you any favor with a finicky female. A mobo starts to be useful for cruising, in my opinion, only when it's big enough to have really effective stabilizers. Or if it's a power cat. I'm sure some trawler
sailors will voice some objections at this point; I hasten to add that this is only my humble opinion.