The DVD/Blu-ray will contain the 60 minute Special plus a 20 minute behind the scenes Doctor Who Extra detailing the making of the episode, plus a 10 minute featurette titled 'Adventures of River Song'.
You can pre-order it on Amazon right now, for £12.99 on DVD (pre-order here) and £15.99 on Blu-ray (pre-order here). The Husbands of River Song will be released on 25th January 2016. If you're not a fan of the standalone releases, it'll presumably be bundled into the complete Series 9 set, which will be released later in 2016.
[Source: Doctor Who News]