Redundant Switching

I am looking to reorganize my networking and servers for added redundancy, and need a quick check to verify that this will work as I think it will.

The plan is to have 2x 24-port switches (NetGear GS724T, sadly, but it's what we have) as the "core" of the network. Each of these switches will connect to a different physical interface on our perimeter router/firewall, with the rest going to the servers (VMware hosts w/ 2physical NICs each on the same vSwitch). This part I am 99% certain I understand and can make work easily enough.

Then, I want each of our 3 workstation switches to also each be cabled to both core switches. This will create a loop (Core1->WorkstationSwitch1->Core2->Core1) and I know that loops are bad unless otherwise configured.

Is this the best physical design, or is there a better way? If this is the way to do it, what is the best way to handle that loop? Is it just STP (which we don't have set up but probably should), or is there a more explicit way to set these up?