Star Cruises is another one. Just been on one this year and can recommend them. You have the choise as to whether to go to the main dining room or the more casual dining area. Even in the dining room it's not essential to get really dressed up. Neat casual dress is acceptable.
I have been on ocean village twice im 43 married with a 10 and 15 year old it is fab recommend it nb i did carrabean cruise would go agai.
RCI ships have a buffet choice ,eg,Jewel of the sea.
NCL is all 'freestyle' so are the two 'Island Cruise line ships' Most other larger shipping lines now have main dining but also 24 hr buffet dining so you can skip the 5 course table and eat in comfort in the buffet restaurant.
Royal caribbean are ideal too. You do not have to go to the formal nights, just as we chose not to. There are so many other restaraunts you can choose from where you can be as casual as you like.
Ocean village is great but we have also been with costa and they have other places you can eat without dressing up.
Most cruise lines have the option of not doing formal - the buffets on Princess and P&O are there for that specific reason on formal nights, and there are speciality restaurants as well.
Why not try Norweigien Cruislines- Freestyle Cruising- choice of several restaurants, no strict dress code. You can of course join in the fomal evening if you want to but many do not..
Try Island Cruises. Great food and informal dinin.