A third alternative would be to find nocks that fit, although I don’t know if that is possible. Probably worth a look.
I have tried both of your solutions, and prefer adjusting the size of the serving, for the reason you mention. I have never been happy with the results of squeezing the ears of the nock together, and it probably does weaken them some.
You can buy serving in different sizes, and might have to experiment a little to get the correct size. I think the standard size is about a .021. It is a little intimidating to do the first time, but really easy once you get the hang of it. If you have a really skinny string, you can double up, like putting a .019 on the bottom and a .021 on top.