First off, do you plan to remove and replace the entire floor? If so, you might be happier using the same general fabric weight as the canopy - making allowance for the coating on the floor. It may just be an aesthetic thing, but generally, a tent feels better to me if the floor fabric is the same or slightly heavier than the canopy fabric. Seattle Fabrics has 1.9 oz silnylon which may be worth considering for reasons discussed below.
Patching the existing floor with silnylon is a good idea. It's a lot easier than constructing a new floor and as James says, a good coating of silicone will make it less slippery.
If you decide to replace the complete floor, carefully remove all the stitching and use the old floor as a pattern. Make careful notes and drawings of how it is put together. In particular, put the coated side on the inside if using PU nylon or 1.9 oz silnylon (which is one-sided like PU nylon).
Be advised that 1.1 oz. silnylon is much less abrasion resistant than PU nylon of the same weight.
The advantage of silnylon is that it won't degenerate and flake or peel off like PU. With care, a silnylon floor will last as long as the rest of the tent.
Depending on the use you put the tent to and its original design, you may need to use nylon thread. Polyester thread does not stretch, but the rest of the (nylon) tent will. When the nylon stretches too much - under wind load, for example - it will break the polyester thread. Use the longest stitch length on your machine. It will probably still be shorter than the original, but that's ok. Some 4-season tents have 3 rows of stitching on the floor/canopy seam. It's tedious to do, but make sure the seam is wide enough to duplicate the original spacing between stitch rows. It's a structural thing.