Or could I just knit a regular sweater pattern in garter stitch?
I think you could adapt a regular chunky jumper pattern to get something similar. Garter stitch stripes, changing colour on the same side each time if you don’t want to get “dash lines” (I sometimes like it as a design feature when I’m doing garter stitch!)
Do you know the conversion rate between garter and stockinette? Like how many rows and stitches for a garter stitch to be the same size as a stockinette piece?
I only know you need to do more garter stitch rows to get the equivalent length of a piece of stocking stitch - how much more depends on tension. They’d be roughly the same width using the same amount of stitches, though stocking stitch curls in on itself (as you probably know!), so until you block it, it might look narrower than a piece that doesn’t curl.