Actually, I'm pretty comfortable in one of my two suits. Sure, it gets warm, but it actually feels pretty cosy. With my wolf suit I can sit pretty easily. The tail is filled with like... filling material, and is just 'attached' with two belt loops.
My dragon tail, however, is pretty large. It has a skeletal structure in it. I am getting a new one from the same maker, a tail which should be lighter and not drag on the ground. The current one is extremely heavy, and since of late part of the base has 'weakened', making part of the skeletal structure poke out into near my tailbone.
I can sit in my wolf's suit rather easily on all types of chairs, etc.
My dragon suit is another story. The tail prevents me from sitting. Unless there is a stool of some sorts, a chair without a back support. It is also difficult to just sit on the ground with it too.