Not steel but my one remaining 26" bike is a 22" Kona Hoss Deluxe which i have singlespeeded at the moment. There is one (frame only) on ebay (a little bit tatty though) which could probably be had pretty cheap i'd guess. I use mine as a play bike and spent the weekend on it with my 11yr old nephew jumping off anything we could find and down all the local steps (although a 24" drop is knarly enough for me)
I'm 16st (without kit) and always ran my seatposts waaay out on my old 26" bikes and never bent one – i've always wondered how people do bend them unless they are very heavy or in a crash/badly landed jump.
At least try and find yourself a 29er to have a go on before you make the decision, you can always sell the wheels you have.
I also just built up a 21" Inbred 29er and those are steel (heavy though) but it seems like a nice fun bike so far.