Internal SSD, Jonsbo N3, LSI LOGIC SAS 9207-8i Storage Controller

I have Unraid installed in a Josnsbo N3 with 8 (3.5) drives connected via LSI Logic SAS Controller. I was wondering if it is possible to connect two additional small form factor 32 GB SSD drives (or NVME) to put the OS on internally. I am pretty sure I can mount them to the side panels ,however I am concerned about heat/airflow, so how small of a drive can I purchase to limit the impact on temperatures. I am concerned regular-sized 2.5 SSD's will obstruct too much airflow...Thanks in advance for the recommendations.