For protein - maybe try some cut up cheese (soft) and avocado (not sure if you tried that yet). Also, not sure what your doc says about when to give your DS eggs, but if he is ok with it, scrambled egg and hard boiled egg yolk are good sources of protein that he may like. (I didn't give my DS egg whites until a year, but I believe at 8 months I was given the green light for egg yolks).
Have fun with it!!