Pea protein is decent. Whatever you choose, just make sure it has a complete amino acid profile and it has more than 2.5 g of leucine per serving within said profile.
Whey is so popular because it has one of the highest amounts of leucine per serving.
That being said, a dairy allergy really shouldn't be triggered by something like whey isolate because everything but the whey has been isolated out, thus the term whey isolate.
Most are sensitive to dairy, myself included. I avoid milk, cheese, creams etc, but still use whey iso.
Have you considered another source of allergies, a compromised immune system or possibly septum issues like a deviation?