i never thought about growing lettuce in pots. would you keep them in the house or greenhouse?
the arugula and romaine might have survived if i covered them during the coldest nights - i found leaves that were still looking good on both of them close to the ground. They must be pretty cold tolerant because it got down to 9. i’m thinking of possibilities for next winter...i miss my free salads!
I have grown spinach and lettuce in the house during the winter in front of the patio door - with the greenhouse, I would move them out there as soon as possible.
New Zealand spinach (not real spinach, but similar) does excellent indoors.
I have grown lettuce and spinach outdoors even during snow filled and below zero. At the first frost, I cover them with row covers, and if the weather gets really cold, cover that with straw-the row cover makes it easy to raise up the covering and harvest the crop.
Plus on warmer and sunny days you can simply roll it up a bit and let the sun help kill any tendency to damp off or mold. The row cover lets it breathe and get enough sun that you don’t have to do this though.