omg, I don't even know you or your dh but this is just making my blood boil. Where does he get off "letting" you do anything?? You're not "his" to "let" You're not asking to use his truck - heck you're not "asking" him anything. You're nursing your child. You're providing the absolute best for your child. ugh.
My response would be "you don't get a vote". End of discussion. And I know that might not sound fair, but that's exactly how I feel right now. Perhaps I might have better advice in a while.
gosh, he's only 8 months old - still so tiny. Even at 10 months old, they are eating so little solid food that rice milk would have a negative impact.
Tell your dh that an allergist should give allergy advice and a peditirician should give infant health advice, and a Lactation consultant should give breastfeeding advice.
ETA: I don't mean to sound harsh I think I should have waited before I posted