BT and NOW TV HD Add-on
BT HD and 4K and NOW TV HD Add-on
For your package the above 2 are available, both at £5, they supply NOW TV HD (Boost) + Sport/AMC HD and 4K or without 4K. Cancelling that means you lose the lot.
You're keeping me on my toes here at least haha.
So yeah you're right you can either have:
NOW TV Boost £3
BT and NOW TV HD/4K: £5
Would you like to cancel the latter and take NOW TV Boost?