We are on the wishlist for 2020 Southbound. We always arrive early, and I think there is more to do around Monte Carlo than Malta. The Med is more of a lake than an ocean, so I don’t think it is very rough often. Luck of the draw.
Second thoughts. This is a sailboat. If you have ‘motion’ issues you may want to think about it.
And, if you google the ship there's a website that indicates all cabins range from about 120 - 145 square feet.