I think Ivan pronounced either way is lovely, and particularly the way you intend, OP (which, as established is a perfectly valid pronunciation is many parts of the world and not "incorrect" at all!
)
This is interesting to me because it brings up the question of how much of a "name" is in the pronunciation (vs the spelling). I'm Canadian, DH is English - many of the names on our list we pronounce slightly differently (heck, he pronounces my own name differently than I do!). When you factor in his Welsh dad and Scottish grandmother, it's likely that any name we choose will have at least two pronunciations just within our family.
Which is all to say, how much would it bother you if others didn't get on board with your pronunciation? Say, when he's a teenager, if your DS got sick of correcting people and was happy to be "Eye-van" to his mates at school and "Ee-van" to his family, would that be terrible? It's all in knowing how much variation/bother of correcting people you can personally take.
That said, I agree with PP that once told, most people should be able to get on board with your intended pronunciation - it's not that difficult!