You may want to try a Wishbass neck....I've been whining for years, saying "I wish fretless necks were thicker!". I've argued that a fretless neck that's just the same manufacturer's neck, but without frets, is too thin.
What I wanted was a fretless neck that would have the same measurements as a fretted neck (measuring from the back of the neck to the top of the fret). This would add a small amount of thickness to the neck (the thickness of the fret being taken into consideration).
The best fretless neck I've played, so far, is the Warwick Corvette Standard Fretless, and I like it best because it's thicker.
Seriously though, while the current trend in all things is thinner and more shallow necks, there are a number of luthiers who will be happy to make your bass in whatever neck thickness, width and shape you desire at a price that's roughly on par with an American Fender.
My personal preference is for wide-but-shallow 4 string necks and I've acquired 4 basses like that.

