I use the belt and suspender system. Works a treat.
For my part, I just use a substantial leather belt and have sewn loops at one end of 2 lengths of 50mm wide black elastic. The belt passes through these loops. The other end of the elastic will be taken care of below.
For the thigh armour, I have cut small squares of syrene (we call it plasticard in the UK), 1mm thick and maybe 2cm square. I have then mounted the male part of some camping snap on this. Then used E6000 to glue these squares to the inside of the top of the leg armour.
Back to the belt. Put it on and also your leg armour. Meaure how long the elastic which is danglig from your belt needs to be, to provide a bit of pull, but not being fully stretched, and mark the position where the female camping snap will go. Take it all off and sew the end of the elastic double, then mount the female part of the camping snap on your mark, facing outwards.
Now you put the belt on, pull the leg armour on and snap the snappers into place and hey presto, stable and comfortable.
Hope this helps.