A dressmaker’s pattern can be a big help. For instance, I have drafted a Knit Radar pattern for a large cardigan using Butterick B5049 by Connie Crawford as a reference
I used this pattern for the armhole and shoulder line. That was all. Almost everything else I changed. Connie Crawford knows that more padding around the middle does not make your shoulders any wider. In this multi size pattern, the width of the shoulder seam is the same for all sizes. The armhole increases in depth and slope with increasing size. If you would like a more complete description of the process of making the big cardigan, and you are a Ravelry user, it is a Ravelry project
If you are looking for interesting design lines, you can find guided inspiration in the pattern books. Vogue 1476, a Miyake design that has never been out of the collection since it was published in the early 80s, includes a shirt with an interestingly shaped back that I noticed repeated in a design by popular knitwear designer Sally Melville. There are other great knittable Miyakes, but they out of print. You can get some idea of the shapes from this website showing the envelopes of most of the Vogue Miyake designs
Some of the Vogue patterns of Marcy Tilton have shapes that would translate well into knitted garments. They would show off fancy stitch patterns and textures too.
You can also find patterns easily adapted to knitting on the internet, take a look at this take on the wrap with sleeves idea.
Happy to use a paper pattern, except you already have a perfect jumper and no pattern for it?
Here's a technique you can use to make a pattern without cutting up your garment. In the clip, David Coffin copies a shirt, but we can adapt.
There are three ways to approach using a paper pattern to guide your knitting
i. You can knit pieces in the traditional way – make sure you adjust seam allowances and hems.
ii. You can go over to what some would see as the dark side and go the full cut and sew from lengths you have knitted.
iii. Or you can take a middle way, knitting parts of your garment approximately to size, and cutting and sewing things like necklines. This works for me. Probably best not to try it on your Show entry.
Have a browse through your pattern collection – it may open a whole new knitting vista.