I think prescription food/therapeutic diet would be best, as your vet has recommended.
Otherwise, ask your vet if this will meet your criteria?
https://www.k9ofmine.com/best-low-sodium-dog-food/ excerpt below
Purina Pro Plan Focus Sensitive Skin & Stomach Salmon & Rice Formula
About: Pro Plan Focus is a salmon-and-rice-based recipe that is designed for dogs with stomach sensitivities or food allergies. Salmon and rice are typically not allergens and most dogs are able to digest this food easily.
Price: $$
Features:
Salmon is the first listed ingredient.
Made with antioxidant-rich ingredients to help promote immune system function
Fortified with omega fatty acids to ensure joint, skin and coat health
Made without any artificial colors, artificial flavors, corn, wheat or soy
PROS: Purina Pro Plan Focus has the least sodium per calorie of any of the five foods recommended here. Most dogs appear to love the taste, and it may also provide some relief from food allergies.
CONS: Additionally, Pro Plan is made without any probiotics to help regulate intestinal function; however, it does include prebiotic ingredients, which can help support any beneficial bacteria already present in your dog’s digestive tract.
Ingredients:
Salmon, Canola Meal, Brewers Rice, Barley, Oat Meal, Fish Meal (Source of Glucosamine), Animal Fat Preserved with Mixed-Tocopherols, Salmon Meal, Dried Egg Product, Brewers Dried Yeast, Natural Flavor, Inulin, Fish Oil, Salt, Vitamin E Supplement, Potassium Chloride, Zinc Sulfate, L-Ascorbyl-2-Polyphosphate (Source of Vitamin C), Ferrous Sulfate, Manganese Sulfate, Niacin, Vitamin A Supplement, Copper Sulfate, Calcium Pantothenate, Pyridoxine Hydrochloride, Vitamin B-12 Supplement, Thiamine Mononitrate, Riboflavin Supplement, Calcium Iodate, Vitamin D-3 Supplement, Menadione Sodium Bisulfite Complex (Source of Vitamin K Activity), Folic Acid, Biotin, Sodium Selenite. J-4449.
Sodium Content:
50 milligrams / 100 Calories
