Bluemoon Nick and I are obvious Thomson converts, I am going on another in March and part of the deal that I booked I got an AI drinks package too with the Island Escape, so thats worth having.
Thomson either on the Med or Carribean are very informal, they have the captains dinner, and you can put on your best suit/frock if you chose to, some of ladies like to wear the sparkly cocktail type gowns for this, I usually just wear a summer cotton dress along with with many others too. There are usually a few restaurants on board, the self service 24 hour buffet one and then a restaurant that you receive waiter service and and then one which usually has a small cover charge. There are 3 or 4 bars on board, with entertainment in the evening in all forms, piano bar cabaret, Mr & Mrs type contest. live music quizzes, bingo, all sorts. The cabins are dependant upon how much you want to spend and how high up you need to be, generally speaking the higher up then the more expensive it will be. In March I have paid a bit more and have a balcony cabin, I love the idea of fresh air in the cabin.
The staff are lovely, well I have found them so and whilst tips are included I tend to seek out the staff that have personally made my trip worthwhile and thank them personally with a gratuity.
Reference booking, I tend to search on the net and get the best price I can then I either go into the local Thomson shop or this time I phoned Thomson direct and they price matched and gave me the AI drinks package.
If it's small and friendly yet still have plenty to do then Thomson may be the answer - I understand that Fred Olson are also very good, I personally have not tried them their prices for solo travellers are not that good for me.
Hope that this helps a bit, if you need any more information then let me know.