When we lost our two in 2005 (one to cancer, the other to old age), we ended up getting two from the pound. Heidi and Molly. Molly (in hindsight) was a nut case and she ended up running away and getting killed. She always forced herself on Heidi. Poor girl tried to crawl in our pockets to get away from the wiggle butt. After we lost Molly, we got Sadie - same breed as Heidi, just a bit younger and those two play incessantly. Both of them instigate the play and it is easy to tell that they are happy together.
I'm not sure that I would upset the routine of an 11-year old senior citizen dog. Can either of the humans in the household include him more so he isn't alone as much?