My vectorised watercolour painting gets blotchy and looses the watercolour details

Michele is right, you will never get all the subtle watercolour details when vectorizing it.

Try to find out what resolution you need at the size you want it printed on textile (you will lose some fine detail anyway) and use Photoshop.

Using the tracing functions on something like a watercolour image is not likely to produce a good clear image, unfortunately. Tracing works best on simple shapes and forms. But you could get better results by scanning in an extremely high resolution image. The problem is that you will have to have a computer with a ton of RAM, anchor points galour - a nightmare. This really isn't what this function is for I'm afraid. Something like this you would want to learn how to repaint, which will take mastery of various watercolour paint brushes. But if you are trying to create a textile print, I would think that perhaps sticking to Photoshop and working with Index colors would be your best bet anyway.