Hi Darren,
I have done exactly what you are talking about, and have experimented with different types of alt-az mounts. I came up with a home-made version which does a great job, but is slightly bulky: but I have ended up with a Stellarvue M2 mount which I got 2nd hand from this site recently. The M2 (and my home-made version!) works very well for both my 4" and 3" scopes, and is smooth even at 200x.
I have a "spare" Stellarvue ED70 that I will eventually put up for sale; just haven't got around to it. This is a very nice scope for grab-and-go and wide-field stuff, and up to around 140x. Drop me a PM if you are interested...
All the best,
Dean