Is there a possibility of using initials? I don't know if your preferred name has the same initials as the name on your financial records. But maybe that's an option. Order however you want, and then the ship-to address can have your initials. I have heard that paypal is not great for trans folks, however, as far as revealing legal names.
For things being sent elsewhere: I would say that if you would be able to have one person pay for it (credit card) on behalf of another person, that could be an indicator of whether one's legal name would be disclosed. For flowers, find a place that will let you write the card out. The recipient might still be able to see the invoice, but you can ask about that. Instead of using a huge online service, find a local place and talk with them.