BT Sports is an addon to any BT TV package, so you would need a base promotion to keep your BT Sports running.
You could downgrade to what's known as the 'Entertainment' package which has 20 premium channels, you currently get 28, so that would save some money.
What you paying now ? Entertainment Plus standard price is £11.50, BT Sports on BT TV is £6.00, so another option could be to see about upgrading to Max HD as that includes BT Sport free and it's in HD, It can work out cheaper combined then having the sport as an addon.
Ring the loyalty team on 0800 800 150 and discuss what promotions are available.