If it's ADSL then it's very straightforward and you can use pretty much any ADSL capable modem/router as Sky don't use any uncommon standards on ADSL. DHCP Option 61 is only relevant for VDSL on Sky.
For ADSL, it's just the usual PPPoA, VPI = 0, VCI = 38, VC-MUX and CHAP authentication. Sky won't give you the PPP username and password if you call them, however you don't need them. A username of "install@o2broadband.co.uk" and a password of "install" will work fine*.
With regard to the W9970, I don't doubt it will work, however it is only Wireless-N, not AC like the Sky ER110, so you may find it is a bit of a downgrade in terms of wireless performance.
* The reason this works is that these are the credentials used when an O2 broadband router is first connected, so need to work in order that the routers used by ex-O2 customers continue to work after O2 Broadband was bought by Sky. If you prefer, you can extract your actual Sky username and password using a procedure like this
https://www.georgebuckingham.com/sky-fibre-router-vdsl-password/ and then use these as your PPPoA credentials, but this is by no means necessary.