Not sure if this has been noted - are you actually wearing a sword or just putting a number one together? If the former, you'd be better off buying sword frogs. There's also protocol for how to hang the sword, but I'm guessing/hoping that you're not actually adding a sword, so I'll skip it.

To echo what Richard said - military (as in actual MOD issue) doublets sit above the hips, which is usually not an issue for high waisted military kilts. I find that if the doublet and belt are snug, stuff doesn't move around too much. A belt around the bottom of the cross belt and tightly wrapped plaid on top (I'm not a fan of the belt over the plaid) will keep you bundled it and won't get shifted too much when you tuck your pipes.

Few things feel as secure or look as good as a Number 1 uniform that fits well and is worn correctly. Unfortunately for a lot of pipers outside the military, that's a rare combo. Just take a close look at most of the bands that still parade in full dress... it's rare that they pull it off (and don't get me started in the half civilian/half-military stuff.... Ugh).

Another source for cross belts - see if anybody is selling old drummers cross-belts. They're kind of a white elephant these days, as they have a steel ring on the bottom where the sword would go if you were a pirate or a drum in the days before drum harnesses. They tend to sell cheaper than standard Piper's cross belts, but as far as I can tell they're just about the same. And I'm sure a bolt cutter could sort the ring out right quick.