hi there
Just to let you knaow straight off that a lot of rescues don't like indoor only homes, but if you contact the local ones they may have a cat that *needs* to be inside due to disability (deafness etc) or FIV (feline aids) and these cats can live perfectly normal lives, just need extra security.
Otherwise there are also breed rescues if you don't mind a slightly older cat needing a new home.
Cat Chat Charity - The Cat Rescue and Rehoming Resource is a good source for breed related links.
One thing I can definately say is Indy (my moggy) is *so* much happier since we got a second cat, it is unbelievable. Even though his is close to our dogs and I work from home another cat just gives him an extra dimension to life and a chance to socialise at kitty-leve so would definately recommend a pair if you can, only costs around £7-£10 a week more yet can avoid the possible emotional issues if you have to leave your cat alone for 8+ hours a day.