You can stay with PN even out of contract until you switch?
Alternatively, I assume by BT FTTP you mean going with BT itself? If you're willing to go BT Business, they're running a fantastic Black Friday deal for £39.95 and a 5G SIM which is of course an EE unlimited SIM, which is billed as £26.95 for broadband and £13 for the unlimited SIM.
If FTTP comes in your neighbourhood, they'll upgrade you without penalty when you switch to FTTP, at least that's what they told me and they seemed super keen to upgrade everyone if they can. In the meantime, you'll have both FTTC and 5G provided you get yourself a 5G router.