It depends on where you would like to go, to be on the safe side I would avoid crossing the Atlantic or sailing out of the UK and try a fly cruise. I would suggest Emerald Princess doing a 12 night cruise in the Med. She is a new ship I went on her last year doing one of these itineraries and had a fantastic time. I would also suggest to go on a lower deck mid ship.
Would recommend P & O everytime - can always remember the `Wow' factor of the band playing, sipping champagne, sailing out of Southampton on first cruise on Oceana. We were advised to go for decks 8 to 10 midships and have always had an outside cabin with a balcony and been perfectly satisfied with this position. Nothing nicer than sitting on your balcony watching the ship arrive or leave port. (Fly cruises often have delayed flights etc!
No doubt about it. P&O or QM2. Stick with the quality end, all these companies ships are stabilised and except for odd biscay crossings in January and February you will be fine.
I suffer from sea sickness and always try to go lower down and mid ship.
You feel more movement the higher you are.
The larger the ship, the less likely you are to feel movement and all modern ships have stabilisers to minimise the effect of rough seas. My wife and I are both in our fifties and we prefer the large cruise ships. We were apprehensive initially but need not have woried. Yes, there are more passengers but equally there is more space in which to carry them. The Berlitz guide to cruising gives a useful statistic for every ship, namely the passenger to space ratio which will give you a rough idea of how crowdwd the ship is likely to feel.
Big ships do not have the intimacy of smaller ships and on QM2 for example, you will find a different atmosphere to the club-like feel you probably experienced on Braemar. However, big ships have more to offer in the way of facilities, for example state of the art theatres as opposed to lounges which contain a stage.
In respect of which cruise line you should choose, we have sailed from Southampton with Royal Caribbean, P&O, Princess and Cunard, and do not necessarily have a particular preference. In the end, it will boil down to your personal tastes which you can only relate to a particular ship or cruise line after you have been on the cruise!