Want solution for attaching SSD drive to Thunderbolt (1?) 2011 iMac

I want to know if it is possible (=how and what parts involved) to attach a garden variety SSD drive/enclosure to a 2011 iMac which lacks USB 3 port and has older-style Thunderbolt (1?) ports along with USB 2 ports. Further, I want this external drive to be bootable. I already have internal SSD +HDD (that works fine), but want to experiment with OS booted from external drive. I can boot USB-2 attached drives, but that’s got limitations.

As I search now for Thunderbolt enclosures, I find only USB-C style (Thunderbolt 3) and a very few older/expensive Thunderbolt-specific drive enclosures (I’d like to attach a single 2.5” SSD so I’m looking for an alternative to this.)

Any suggestions appreciated!

Dave