You can always blacklist a package (such as linux) in /etc/pacman.conf to avoid upgrading it during pacman -Syu, for example. I had to do this during a power regression in the kernel. However this isn't a long term arch strategy. Note also that arch has LTS kernels, should you prefer.
If not upgrading the kernel every week or two is a security hole, most people are pretty screwed. I personally do not like to restart that often. Turning off automatic updates just gives you control of when to upgrade.
