I didn't find any adapter suited for the setups I usually do so I made this one. It is minimalist, can be printed on the tiniest printer and does not need support. It can handle up to 2 ssds (in place of the 3.5" spinning drive), perfectly fits the iMac mounting bracket and allows good airflow. The 2nd sdd has a 10mm offset to be able to fit right angle Sata & Power connectors on both drives if necessary. 2009-2011 iMacs have 3 Sata/Power connectors (1 for HDD, 1 for ODD and 1 for optional SSD). You'll find the special cable for your model at the usual place for a few bucks...
Edit: I fixed some dimensions, strengthened and added screw threads to the mounting points.
The author marked this model as their own original creation.