Advice on modem when upgrading to FTTC?

I'm planning to upgrade from ADSL to FTTC, and I'd welcome any advice on how to carry on using my Asus RT-AC87U router. Can you recommend any ISPs whose supplied routers are easy to switch to modem-only mode? Or should I just buy a third-party VDSL modem, and if so, which one?

I'm currently with the Post Office but for a modem I'm using a Sagemcom 2740N originally obtained from Plusnet. Getting it into bridge mode was a bit of a faff, and I'd like the change to fibre to be simpler if possible. For example, I see that Virgin's current routers are easy to switch to modem-only. I might stick with the PO if their fibre router is any good as a modem.

Thanks for any ideas.

Charles

PS I hung on to the Sagemcom 2740N after moving from a long line in the back of beyond. It worked like a champ, outperforming both Billion and 2-Wire (the old BT Business Hub).