Hi,
Very sorry to hear about your furbabe. I went through exactly the same situation 2 weeks ago. We had 2 boy cats, only 15 months old, they were inseperable and brothers, but chubchub got killed by a car and Mouse was inconsolable, he was absolutely devastated. A few days after he started to get a bit better, he got a whole lot of attention, new toys and cuddles. He's still not fully over it, but i don't think he ever will be, but it does get easier to bear for us and Mouse.
When the time is right we'll be getting him a new friend too, can't get a kitten though as Mouse is an indoor/outdoor cat and i don't want to stop him going outside or stop him coming inside when a kitten is around, so we'll get one around 4 months old so it wont be long before they can both go out.
We'll leave it until the new year though, want to give Mouse time to grieve first, he's been through alot in the last two weeks, his whole world's changed, so we don't want to put added pressure on him by bringing in something new.
Hope it all works out for you and your babe.
Beth & Mouse