The Aldi pair had an interesting design, in that there was no elastic across the front waistband. Instead, there was a doubled over yoke, similar to a maternity panel. I guess if you are sitting on a bike, there is no chance of your pants falling down, so this seems like a comfortable option. I got out my pencil and paper and drafted a pattern with this feature. I also included a side panel with a big pocket, in case the chamois didn't work out and I decided to use these for running instead. This time, I used Jalie 2920 as my block for drafting. It is a one piece pattern, which makes drawing on design lines easy. Then it is just a matter of cutting up the design lines and added seam allowances.
Front panel (lining up with side pocket)
Inside view of front panel
Inside view of back, showing elasticised waist
Large phone pocket
I only go cycling once a week, and I've actually missed the last couple of weeks, so I can't even report whether or not the chamois improves the cycling experience! I've only attached it with a wide zig-zag in case I need to re-position it.