For a/c, the absolute worst thing you want is a unit that is oversized. Before you do anything, you should have a heat load analysis done to see what size unit you really need for both heat and cooling. Then, using that, determine what you want to do. It may be that the smaller unit would work for the whole house and the one you have now is oversized. Running it at or near its maximum output constantly on the coldest (or hottest) day it's designed for is the most efficient and comfortable.
I think R22 won't be available for sale (new anyway) shortly. recyclers will likely still have it, but at potentially very high prices in the future. Now, the system should not need any, but if it ever does (say you decide to replace the compressor rather than replace the system), it will start to become a very expensive proposition.