A stand of some sort for your
WSM would probably be the easiest, I'm not sure as I haven't ever seen one except in pictures. I haven't seen a smoker that won't put out good food, just some require more work and babying along than others. Be warned, from everything I've read, that if you move from a
WSM, which is almost a set it and forget it smoker, that whatever you go to will probably require more work during the cook than you are accustom to now.
As for the horizontals, don't let a couple of mods scare you away. I've cooked on the cheapest model in Home Depot or Lowes and the food still comes out good. The most you are probably looking at would be a baffle, tuning plates and coal basket. Possibly, depending on the model, some gaskets for the doors. These can be done with minimal additional cost and thought out ahead of time can be built in when assembly takes place. Assembly of these would probably be harder on your back than cooking several times with the
WSM, so try to find some help if you go this route.
Have you walked into one of the local stores and checked the heights of the cooking chambers and fire boxes? You will definitely be feeding the fire box on long cooks in a horizontal. If you post what you're looking at picking up local (so maybe you can get the floor model and save some assembly pain) I'm sure someone here can tell you what kind of mods you will probably want to make in the beginning.