You could try 'actually' or 'in fact'. These are also meaningless fillers, but they make you sound slightly more authoritative than 'you know'.

I'm not sure that I'd agree with that. I typically only use "well you know" when I actually want to confirm that the person does know something. You will then typically get a nod or some clarification from the person you are talking to if they agree they know it. Now there are plenty of phrases that can be used to fill a gap while you think bu they all have some meaning. The simplest is probably simply Ummmm, this has no meaning except that you are pondering a response. I guess, I suppose, but like I say they have meaning as well. If you could be more exact as to what you want I might be able to help better.