Do yourself a favor, at least get the full upgrade kit from OWC
with the inline temperature sensor replacement at a bare minimum.
In terms of a drive, everyone seems to jump on the OWC bandwagon,
and while good, they are pricier than other alternatives, which will
work just as well. Personally, I have used Sandisk, Toshiba, and Kingston
drives in various Macs and all work great. They may not be the bleeding
edge in speed, but they are still leaps and bounds faster than HDD and
at somewhat more lower price points.
I also suggest, getting a USB3.0 case or USB3.0 to SATA adapter and clone or
install fresh macOS on the new SSD via that and test for an extended period
to insure all works well before "cracking you iMac". Or, if all works well,
simply just boot from the external and resolve the whole issue of "cracking
open" the iMac. The SSD may not be quite as fast as if it were internal but
will still be much, much faster than the internal HDD.