I am so very sorry for your loss
I lost my older boy last year, (15) and his long time companion, my Maltese, went through a depression of sorts, that manifested itself physically. It was hard for her, even though she has 3 younger companions, she missed him terribly. It took some months, but she is much better and has bonded with one of them.
Just like us, animals grieve, and how they do is different for each one.
Only you will know when and if the time is right for a new furbaby, there is no right or wrong way. In the mean time, spending special time with your little guy, bonding time, more activities together may help him.
So sorry for your loss, May your boy rest in peace