Can I ask why you only want activities for home? Why not get out? Maybe there is a moms group you could join. Moms Club International and Holistic Moms Network are both great organizations you could google to see if they have chapters near you. La Leche League is great, too. There might be yahoo groups in your area. The community college may have a coop preschool group for babes or there may be something at a local church.
When my dd was five months, I made it a point to get out of the house daily. I joined two mama groups. Sometimes I even just went window shopping just to get out. I love my babe endlessly, but there is only so much baby fun you can do before you need a little different kind of stimulation. It was fun for her, too, to get out and make friends. We still play with two of the boys from those early mommy group days. (she is now 33 mos)
If you really want activities for home, try infant massage. You could most likely get a book or dvd or video from your library or there are directions online if you google it. Or, take a bath and just play in the water. Or, read stories. Or, bundle him up and go for a walk. Let him interact with nature. This was my babe's fave activity at five mos. Or, you might go to the library and ask the librarian to help you find books about games and activities for babies. They are out there but a librarian could help you find them quickly and easily. I used to read a lot when my babe was napping in my lap.
Hope this is helpful.