I don't sell this product or even advocate it but it's probably worth looking into - Skim Coat and Drywalling Tools. BUT, this is getting ahead of ourselves. This WEB page DOES have a picture of how their 'tool' handles textured walls. (Not bad ...)
You can to Builders Book Site, select their Search option, then select the 'Carpentery/Const Tech' option from the pull-down menu. You'll get 6 pages of stuff on the subject, and about 2 or 3 pages or so into it, you'll see specific books about drywalling.
The key will be lots of thin skim coats with intermittent sanding between them. It's not hard; just time consuming. Natural light is best for seeing imperfections. My best to ya and hope this helps.