You don't have to take any action now. Just remember you can't "ditch" cobra mid way outside of the enrollment period. For example, if it runs through September 2020, you can't decide in April 2020 that you want to give it up and go ACA. However, you can always dump it during open enrollment. That's what I did, but I was only dropping the last 2 months.
You can, however, enroll in the ACA outside the enrollment period if your Cobra ends outside. So, let's say your cobra ends on July 17, 2020, you are eligible to enroll in the ACA as an Event, just like if someone lost any job insurance, or if you had never gone on cobra to begin with.
And yes as noted, if you are on cobra for part of next year, then go onto an ACA plan for the other part, any contributions toward deductibles in your cobra plan will mean zero towards your aca plan, even if you stay with the same insurer.
ACA plan starts enrollment in November I think, you would be wise still to shop and have a look.
ETA: with my MC, when I was on cobra, I still had to do the regular insurance annual enrollments as if I was still employed. I got the same packet and choices, etc. So there is that, but not the ACA marketplace stuff, to do.