Cat food

Great to back (had uni so haven't had time to come on)

Basically i've got a senior cat (13yrs) and he always loses a large amount of weight in winter and we struggle to keep the weight on him. Not only this he is a very fussy cat and also suffers from eczema (obviously not helped by the cold).
I'm just wondering if anyone knows any brands of food which will suit him, i've tried him on:

Royal canin skin and coat (he does like it but i would like to try and get better due to the wheat etc. in it)
JWB - he loves it but can't keep weight on (haven't tried kitten yet though)
Applaws - he hates but it suits him, obviously as he's not eating it he is losing weight but his coat is in amazing condition at the moment)
Purely - he liked but he couldn't keep his wait on.

I haven't tried science plan as i'm not particularly a fan of the food as its more expensive than it's worth but the vet uses them as treats for him and eats them straight down, has anyone had a strange cat like mine who it suited?

I would prefer grain free especially as the foods which he seems to lose weight on has grains in the first few ingredients. He is fully wormed and flead so i'm not worried about that, the vet did just says it's his age but i would like to get him in decent condition, especially with how cold it is.
thanks in advance

I used Purely from them being kittens to about a month ago, and they are now 2.5yrs. Now i feed them raw. It was a bit of a struggle at first as they were shocked and horrifed at being presented with a bowl of raw mince But now they are generally waiting for breakfast and tuck in like mini lions!

They look great on it as well, fab coats, good weight, and literally bursting out of their skin with wellness. Might not suit your cat, but I thought I'd mention it

Thanks, i would love to try RAW as i nearly put my dog on it, only problem is we don't have the freezer space and i still live at home. Having fish, hamster, guineas, dog and cat i've already taken over most of the house so they're not too happy about the idea of RAW feeding

I'm thinking of keeping him on applaws kitten as his coat is great but due to him not eating much just putting a pouch on his food so he gets extra and he should eat it. Looking at simply (feline fayre) as it's cheap enough and 60% meat, not too worried about the other ingredients as Applaws will still be the main food.