A recoil spring with much less strength is likely to transmit a lot more recoil to the shooter's hand, especially in a light, short grip PM9. Have you considered a LakeLine charging handle? (
https://lakelinellc.com/shop/kahr-9mm-charging-handle/) Kahr sells similar units. (
https://shopkahrfirearmsgroup.com/ka...arging-handle/) I have never seen one, but it is vaguely similar to charging ears that come on HK VP9s. I have one and I think this would help someone whose problem is gripping the thin slide, but who has the basic strength to retract the slide for loading. If you try this, let us know how it works for you.