I would definitely do a fairly large sized bed, boxers grow quickly!. I have one that measures about 32x20, then there's a cedar bed inside of it..Samson used to sleep in it all the time, now he never does, neither does Angel, but sometimes she uses it as a pilllow!
my boxer is not crate trained. she however has an very large dog bed i bought at petco. she also has her special "chair" in the living room, any other furniture she waits to be invited up before she gets onto it. i would go with a large bed as others suggested.