Now that I have room to put it in, I am going to buy the cats a tree to climb and play on. This is not an outside tree... these are inside cats, who have never poked their pink noses out the door. It is an ersatz tree, one made of cardboard or plywood and carpet, with lots of opportunity for scratching, climbing, crawling, batting hanging objects, and sniffing.
However, I have an extra challenge. Whistler weighs 18 pounds, which is much heavier than most cats. To give you an idea, Shadow only weighs 6 pounds. That is a bit small, but closer to average than Whistler's blubbery weight. He is large and heavy. So a spindly tree will come crashing to the floor under his weight.
I have to find a substantial tree, well made and with suitable perches for a big fella like Whistler. I wrote to a company that makes these things and has a sale on their present models, asking which, if any, would be suitable for him.