Hello and welcome to the forum. Luckily, there has been a lot of new, high quality dog foods introduced onto the market in recent years so you have lots of choice. Unfortunately, it can be more expensive to feed a dog using wet food than it is for dry.
Using the Dog Food Directory
filters, I did a search and it returned five pages of products. I cannot save the search for you but here are the filters that I used:
Type of food - wet completes
Food properties - natural and clearly labelled
Rating - set slider at 3.5 to 5 stars
Avoid ingredients - all red
On those five pages there are some excellent products so it would be best for you to look down the list and see which ones suit your budget. Some are available in shops - Evolution, Fishmongers and Wainwright's are Pets at Home own products. Naturediet, Natures Menu are also fairly easy to obtain. Forthglade and a new one to the market, Harringtons are both sold in large supermarkets. Some of the others may be available in store too so just click on the Store Finder button if you are interested. Some Asda and Tesco branches have started selling a new fresh food product called Freshpet but we haven't had any reviews on the forum and I haven't seen it myself.
Once you have established your dog on a suitable product that suits his digestion, you might be able to find it cheaper by buying larger quantities online.
Regarding your dog's poo it will be the Chappie that is making him go so frequently. When I have used quality wet food on my dogs I always find that their poo is small in quantity and very firm indeed. They usually only go twice a day. The products that came up on the Dog Food Directory are high in protein and fat so your dog will hopefully gain weight on them. Chappie is low in fat so this could be why he has lost weight.
Please can you let us know if you need any further help and also how you get on? We would be interested to hear of your dog's progress and it might be helpful to others.