Overly affectionate cat

Our cat is 14yrs old, last November we lost his sister who was the same age.
He has always been affectionate, always snuggling up, he was always never far away. But since his sister has gone, he has become obsessively affectionate, he refuses to leave us alone. He has to be on top of us, he has to sit between us (can't be on the side, must be in the middle). He has always slept at the end of our bed, but now it's either in the middle at our head height or literally on top of us. He follows us everywhere.
I figure he must miss his sister, still be grieving. But I'm, we're going crazy with the over affection. Getting him a friend is out of the question, but I don't know how to help calm him and get him back to his normal self..
Any ideas?

Rescue remedy?

Is there rescue remedy for animals? Or should I just use it? (Hehe)

There is something called Feliway that may be of use. Try the vet or a decent pet store

Maybe get his health checked at the vet, make sure he's physically comfy. Maybe he feels the cold more now he doesn't have his furry friend, so a snuggly self-warming bed might be just the thing for him.

You can use rescue remedy on pets. The vet told me to give some to my dogs and cat in preparation for all the travel for our move to Australia from NZ. I gave it to them for a few weeks prior and the cat was sleeping on her back with her feet in the air in the car on the way to the airport! Certainly chilled her out. That was years ago now though, maybe it isn't the done thing now.

If a new cat is out of the question what about going to a vinnies and trying to find a big cuddly toy or some sort or furry, shaggy blanket that he might like to cuddle up to. My cat loves sitting with us but when I had the girls woolen underlay from there bed on the clothes airer inside he thought it was the perfect bed and not spends 90% of him time sleeping on it :)

I would suggest a vet check up too, would not hurt. Also does he gravitate more to one of you or just whoever he can cuddle with?

Thanks guys, I'll ask about rescue remedy and then try it if they say ok.
I can't take him to the vet thanks to how much it stresses him out. I might go get him a heated bed and see if that helps too.
He is my cat, so has always been more affectionate to me, but now he loves the whole family a lot. Last night dh and I were watching tv on the lounge, we were sitting right next to each other, and the cat comes and sits on top of us, pushing a little space in the middle to lay down. I picked him up moved him to my side, he looked at us and went straight back to the middle, and he'll do that every time now.