My Louie has been gone over a month now, and Howie seems very lonely. He's very demanding of affection from me, but at times just wanders the apartment, I think smelling and looking for Louie. I'm going on a long road trip at the end of June, and I think after that I'll visit the shelter. The vet says a kitten is best so Howie doesn't feel threatened, but the kitty should be a little older, like 4-6 months so it can defend itself. She said a boy is best.
But I wanted to see if anyone had any input on age and sex. I've tried to foster an adult cat and that totally didn't work, so I agree a kitten is best.