It does sound like he needs a place to climb. I have a couple of cat trees in our house and also have one room that has wide shelves with outdoor carpeting on them so my two 8 month olds can get up there and run around. It wasn't hard to set them up and the carpeting on them is so they don't slip.
Also, sounds like u need to get an interactive toy to play with him, not just throwing a toy. He needs mental simulus like "hunting" a interactive toy will give him.You need to move the toy like it is prey.
I have heard that first they hunt, (interactive toy) then they eat, then they sleep.
A good book to read is Think Like a Cat by Pam Bennett Johnson...or Pam Johnson Bennett. Can never remember the order of her name, but she is a cat behaviourlist that has written quite a few books about cats and has good tips.
~Friendship is like a bank account. You can't continue to draw on it without making deposits~
~Tegan 9 year old yellow lab~
~Wilbur 9 year old LH cat~
~Mirabelle 18 mos dsh~
~O'Shawnnessey 18 mos dsh~
~Darby 1 year old dsh~
~Mindy 7 yr old shih tzu~
~Dexter 10yr old Salmon (large goldfish)