To avoid 'overtightening' elastic girths whether two sides elactic or just one, choose a girth with triple layer elastic. These are much harder for the rider to pull up but they still allow the horse a little 'breathing space'
Treeless or pny pads are great for the rounder ones! Just make sure you have even wiegth in both stirrups or you may end up under the belly!!:) (can happen with the wider trees saddle too tho!)