I have small hands (see pic for reference).

I’m wondering if an e2 grip will help me reach the magazine release and decocking lever easier with my thumb.

I have standard hogue g10 grips already.

The E2 grip will always be the overall thinnest grip around. How much that will help you, I have no idea.

Yes, however. The however for me was that the E2's were grip sensitive for me during slightly imperfect draws at speed. Replaced with G10's.

I also replaced the Sig standard reach trigger with the GrayGuns Intermediate reach. The combo placed my trigger finger closer to the trigger face and solved the reach problem with no disadvantages.

Finally, be aware of the fact that installation/removal of the E2 grips involves the risk of destroying the Trigger Bar Spring (TBS). Happened to me and a number of other SF members.

Sig also offers a skinny Short Reach trigger. Most, including me hate it. Pinches like hell.

This can give you an idea with regular grips and e2, intermediate and skinny trigger.