If you and your vet are happy with their weight, I would not change the amount you're feeding them. However, my pups need more calories in the winter to maintain their weight.
Treats - my pups love sweet potatoes and raw (or cooked) zucchinis. sometimes dogs like green beans or carrots. at my house, tri-ing is really bad about taking the carrots, chewing them up and spitting them out all over the place. Yea, thanks Jet. Otherwise, they also like cheese, waffles, eggs, etc, but given you pup's allergies, you may not want to try the later.
LOL…. leave it to the "Tri-ing" to make a mess out of the carrots!!!!