It seems to be that using PGP here is going to be too complicated.

Given that, I would opt for Loyce's suggestion of using ProtonMail for its end-to-end encryption. You can make an account for free, and I will supply you with my email address to send the keys to.

If you don't want to trust me then I can try to talk you through setting up and running this tool locally, but you've already said you would not feel comfortable installing and using Linux.