OK, I've read lots of suggestions (some were shot down by the old-timers). Since this is my first batch (brew?), I want to do the best. So, what if I buy commercial mead to use a topper? Or, is vodka best? Or plain water? Or honey/water mixture? Any/all of the above? I'm really confused.
Commercial mead ? Yes that'd work, though it's better if you can get one with at least some of the properties of what's been made or one that you already like (all the commercial ones I've seen here are very i.e. dessert sweet).
Vodka ? Yes that'd also work, but it would slightly reduce the viscosity of what you've made, also it will dry the batch out a bit (both of which can be corrected). It will also mellow with age if it did give you a bit of an "alcohol hot" taste.
Honey/water syrup ? Yes, that also works, but is usually known as a back sweetening mix. You'd have to stabilise with sulphite and sorbate first, because if there's any ability left in the remaining yeast cells (and yes, even if you've got it racked clear, there will be some), then it can start to referment.
The glass marbles trick works, but if you're using a glass fermenter, you have to be vvv careful not to smash the bottom out of it. Plus you'd be surprised how many you may need.
CG's comment about starting a batch in a bucket is valid as it means you can make a batch slightly larger, then once it's dropped a sediment, you can siphon off into a glass carboy/demi-john, and any left over can be run into a plastic pop/soda bottle and put in the fridge, and saved for later for topping up.