Very sad for the lost of your cat, I had cats and dogs with me for most of my life and I know that they mourn. Extra attention and love is important and in time you will know if it's ok to get another pet friend.
My big lab Mozart just turned 11 years old on April 6 (post Happy Birthday Mozart) and even tough he looks yound and he's still active, my hubby and I know that we will loose him and we try to get our minds ready for that. Her buddy Holly who is 8 yrs old will miss him dearly but she will have her cat friend Celeste to look after her.
Give your cat lots of love and attention and if you see that it's too difficult, get him another companion