imo none of the soft putters have the float characteristic you are referring to.
on putts, the disc stays in the air from one or more of the following: raw velocity, glide/updrafts, or clean spin. most soft putters are pliable and seem to carry a lot of mass in the flight plate in order to keep them with some shape and then rely on the flexibility of the plastic itself to absorb shocks. the downside of this is that they tend to behave less glider-like and more like weights. the second part of this is that as they break in, softer "floppy" putters tend to burn up a lot of their RPM's as the disc requires more kinetic energy to get it to spin cleanly/uniformly.
personally, i don't like putters that float and hang in the air (rattler, polecat, birdie, putt'r) or putters that have no carry whatsoever (rhyno).
as for your problems with magnets, it may be the downward slope on the leading edge which causes it to drop. i find that a flat putt with a magnet tends to fly like a nose down putt and it's kind of funny to watch me try to make adjustments to other putters after say, a half hour of putting with a magnet (as all my other putters i end up putting unintentionally very nose up).
as for what you are looking for, i can't really say what will work. wizards float more than magnets and rhynos, but not as well as an aviar. the challenger tends to drop quite a bit as well. you may find a good combintation of flexibility and characteristics with the regular old aviar putt & approach. however, i'm more partial to more stable putters such as the wizard, challenger, and big bead/kc aviar.
i wouldn't get too hung up on stiffness of plastic as generally stiffer putters will hold their line better and have a bit less low speed fade than softer plastics. while soft putters might help increase your make % when you miss slightly right, they also spin putts off the chains that hit slightly left. being able to hit where you want to every time imo is more important than the plastic being soft/firm. i find myself more consistently hitting the spot w/ firm putters and have stuck with them.
as for ideas on what you might want to try:
s/h wizard (h will have more float)
big bead aviar
aviar putt & approach
pro d challenger