Fitting a knitted garment

[Morgan]

Coming at this from a different angle -

I have a garment pattern making softward package (now very old) that can be set for sewing  knitting ir weaving.  Create the pattern, then enter the details from the swatch (stitches & rows) and the programme creates simple row by row shaping.  You maintain the knitting/crochet/weaving pattern but follow the shaping for the row number. It works well. 
Garment Designer
https://www.cochenille.com/garment-designer/
They also have a Stitch painter programme   

Since this software became available, more programmes and knitting pattern generators have been created. Some are more sophisticated than a simple shaping guide.
Some are free some are paid for. 

https://knitanything.com/index.php?route=information/samplePattern

https://app.dreamknit.com/

https://knitsthatfit.com/

There are others.  Ravelry has discussions about these things too 

[Puzzler]

Thanks, @Morgan. I will no doubt investigate these. The app for my iPad is appealing (see what I did there  ) but I never have enough storage space, so every time Apple releases an update, I have to offload what I can. Schematics appear to take into account vertical and horizontal measurements. With a very rounded back, I do not want to lengthen the whole of the back, just the centre, tapering out to the sides as one would for a round back adjustment in a sewing pattern.