I recommend the support. You can really only expect one good clean stroke, because double stamping is vitually guaranteed if you don't get a good impression the first time.
I am terrible about flinching when I take a hearty swing at my fingers with a 2 lb hammer, and consequently seldom have gotten a good stamp (and lots of double stamps), and my expensive die often goes flying across the shop...
But you're right, the fixtures are expensive. Somewhere on here there's a recent post about this very subject and I posted a pic of the fixture I made out of scrap parts around the shop. It works very well, and cost nothing. I won't waste Spark's disk space posting the pic again here, but you can probably find it via search, and I'd be happy to send more pics if you're interested.
One trick that does help is to put a piece of masking tape over the place you're applying your mark, this helps keep your stamp from slipping aside.
Dave