Does the USG support Sky's implementation of MER (I suspect not)?
If it does happen to support MER your best bet is a secondhand Openreach HG612.
If not I think there are some Billion routers that do support MER and can be bridged.
I you want a simple life cancel Sky and pick an ISP that uses a standard PPPoE connection (Plusnet, BT, Zen, etc.).
So you're back to does the USG support MER?
Sky are fine, but they aren't user friendly when it comes to using your own kit.
Many people end-up connecting their router behind the Sky router, and because there's no bridge mode available you end up having to double NAT.
No the HG612 is just a modem. The router behind it would handle the MER side of things.