As no-one guessed the answer to this post, i suppose i'll have to tell you. Although from J3 and Wendy's comment, i found out that SG had already let them in on His mystery purchase.
The latest addition to our toybox turned out to be an Ultimate Bondage Gag Harness, complete with inflatable breather gag - and it's a fairly scary-looking piece of kit!
And SG was keen to use it on me, as soon as He had me back in His lair last weekend...