I have read this thread with interest and I must say I am surprised that only one naysayer has shown up so far. I happen to know there are several folks in this forum that firmly believe every knife worth inventing has already been invented (some would say invented long ago). Hard to believe everyone is being so supportive of such a risky undertaking without even knowing what they are supporting.
Personally, I don't subscribe to the notion that all the good ideas are taken... but I am a skeptic when someone claims to have a really great idea but won't share it (or even hint at it). The implication is that the idea is simple enough that it wouldn't stand up to standard patent application scrutiny. One of the key tests of whether a patent will be accepted is whether the idea is obvious to anyone with knowledge of the trade. And then, of course, there is the prior art search. This isn't about whether a product exists on the market, it's about whether an idea has been described in a patent before the one being investigated.
Anyway, best of luck with this... whatever it is.