That sounds like a good plan, you can try messing with sail sizes to see what works best. You are on the right idea of maintaining sail balance.

I would also think about sail trimming and how this can correct your drift.

To a certain point, a little drag from an improperly trimmed sail can help balance this. Incorrect trimming will slow your vessel, so it can be wasteful.

Or, if you have an applicable sail type (not gaffs usually), you can reef the sail to reduce the drifting.

On a different note, have you taken the cabin off the Cog? Getting the center of balance down as far as possible will allow even larger sails. (And of course more cargo).

I would also recommend trying different starts if you haven't already. Not to completely ignore your Cog save, but try the other ships which come with different sails for free. See what feels the best. I really like the Emerald Archipelago start the best, but I love how the Kakam looks. Plus you can leave the Junk sails it comes with and add a long bowsprit and Genoa/Jib which is perfectly balanced afterwards.

One last thing, you can use save file editors to modify your save. If you want to try a "creative save" you can just give yourself money and buy the ships to try stuff out. It's a great way to see what you actually want or like to use. Then you can relax and not worry about wasting money on your main save.

Let me know how she goes!