I moved into a my new apartment almost a year ago and it was also much smaller then my pervious place as well. I have had to make use of things like storages boxes under the bed and undercounter organizers alot for my most of my junk. Down-sizing and getting rid of my non-essentials really helped as well. I was a bit of a clutter bug prior to the move but learned very quickly that my new place wouldn't allow for that.
My cats however adapted to the smaller space very quickly mainly because of the addition of a kitty recreation unit that made use of height instead of width. I have it infront of my window and it is about 6.5 feet high and had several different levels and features for them to amuse themselves with.
Lastly window sills extentions and a clear veiw outside goes along way in keeping my cats amused also. Mine are exclusively indoor cats but I made a point of putting several bird feeders close to the outside of the window which really interest them. They will spend hours watching the birds eating.