The new thinking behind what to feed dog's these days is that dog's should eat what their ancestors ate, or close to it. That is of course easier said than done. Secondly, you get what you pay for, and that goes for dog food too.
Therefore, try to find a dog food that is as little processed as possible, that contains no rice, wheat, corn or soy, and DOES contain whole meats, fish or fowl. Stay away from "hot or warm foods" in the case of seizures. From an Traditional Veterinary Chinese Medical Stand point: Hot or warm foods can cause increased internal heat in seizures patients. Commonly used hot foods in commercial diets include: venison, duck, beef, bison, kangaroo, potatoes and other starchy vegetables.
Dog Food Brands that I suggest are: Instinct, Taste of the Wild, Halo, Merrick's, Evo/Innova, Wellness, and Nature's Variety to name a few. There are many more good ones out there. Please read the label carefully as all brands of dog food also have versions with foods that may not be suitable. Please purchase what you can afford while trying to observe the guidelines. Try to use only canned versions since dry food must contain some carbohydrate to hold the kibble shapes. Or, try to feed as much canned as possible if you must feed kibble.
There is also a growing trend toward raw diets. If you are interested please check the following link: http://www.dogfoodadvisor.com/best-dog-foods/raw-dog-food/
Your dogs T4 result is considered low for a Post T4 therapeutic level. Please ask your vet if the dose can be raised. His ideal thyroid replacement dose is the one in which he has the most reduction of symptoms of hypothyroid. Excessive sleeping is a symptom of hypothyroid.
There are Chinese veterinary herbal remedies that help as an adjunct to seizure therapy or even as a solo treatment in some cases. These Chinese herbal remidies are less costly than Potassium Bromide. If interested, please check in your area for a veterinarian that is versed in Chinese veterinary herbal formulas and acupuncture.
I had to ask the vet about increasing the thyroid replacement, but once they looked at it they agreed. They suggested that I give him 1/2 pill in the morning with the one pill he is given twice a day. So far he seems to be feeling better. I wonder if it really should be done twice a day.