I want to get a pal for my pooch?

and im looking for a small dog...im looking for a breed thats friendly and can take well to another dog...my dogs a patterdale and now my kids are at school he is lonely..hes the type of breed that needs to be constantly stimulated and kept amused which my kids did plus i cant do all the time ive got to work (work from home)...im happy to get an unwanted dog but im wary about the type of home it will come from (hom here dog has been mistreated)...so any thoughts any suggestions are welcome...he needs a little chum to play with while im busy....and before anyone types...yes im responsible..and it will become part of my family