I’ve been through all this.
IMO you’ll never approach anything like the flotation you can get with proper fat wheels.
The Surly 1×1 can take a 3″ tyre at the rear. Fronts are limited by forks, but that’s easy fixed by getting a fatbike fork or homebrew your own. If you make your own you’ll be able to control the A-C distance so you won’t jack up the front of your 26″ bike and upset the geometry. (No problem with a 29er)
With the benefit of hindsight, start with a fat fork, try your experiments with stretching an ordinary tyre on a wide rim, then realise that it’s simpler to buy a Larry or Endomorph to fit in your fat fork. Don’t worry too much about the back wheel because once you have tried the fat front, you’re going to want to go the same way at the back. The only way to do that is to get a frame that will take a fat wheel.
Or shortcircuit the whole timeconsuming and expensive process and just go and buy a fat bike 🙂
(I’ve now got enough bits left over from my experiments on this that I’ can build a ‘Puglet” – a Surly 1×1 with a 3″ rear and a fat 4″ front)