I have been using Simpson brand "Insulation Supports". I use the 23.5" size. this is extremely strong wire, which is slightly "springy" although it is not spring steel. It is very hard to bend, especially into smaller loops, if needed, but it is nice and straight.
I am very fortunate that my father has a blacksmith shop set up right next door to me, so when I need to I can heat the wire in a forge and work it with a hammer, needle-nosed pliers and an anvil. It cools very quickly, so it usually has to take several trips into the forge, but when I'm done I have a loop that won't straighten out on me.
The UPC # is 0 44315 81481 5 for a box of 100, which I think cost me about $7.00.