Best girth to relieve pressure

[NotTodayJose]

As title says really -

I'm searching for a girth that will take pressure off my horse's lower shoulder area.

She has quite a far back girth area, not a forward girth groove, and the saddle doesn't really slip back / forward so crescent or H girth don't seem quite right.

The saddle she's in has to be girthed up really quite tight to stop lateral slipping to the side so I want something that isn't sore on the sides for her.

Have you had a qualified Master Saddler (not a fitter or salesperson) to check your saddle? The conformation of some horses with flat withers, or if they’re overweight, makes them difficult to fit. But overgirthing shouldn’t be the answer.

As PP has already suggested get your saddle checked by a qualified saddler that it both fits your horse and that you are placing it correctly onto your horses back
I would suggest a soft leather Atherston girth with one end elasticated , make sure that it’s the correct way round , ie elastic is on the RHS so when you have mounted and do the girth up you are not pulling the Elasticated side directly , keep it cleaned so it stays supple and soft .

My horse is in a treeless saddle

If your saddle, whatever the design, is slipping, you need a professional saddler to assess how it fits when your horse is moving with you riding.

Any girth will be exerting equal pressure everywhere it touches your horse.