Voluntarily terminating COBRA early does not create a Special Enrollment Period (SEP) to enroll in an ACA exchange plan.
"If you’re ending COBRA early - Outside Open Enrollment
You can’t change until the next Open Enrollment Period, your COBRA runs out, or you qualify for a Special Enrollment Period another way" (the OP is moving).
Reference:
https://www.healthcare.gov/unemployed/cobra-coverage/
You have your choice of 3 ACA exchange enrollment periods to choose from.
1) After you move to FL you will have a limited-time relocation SEP (Special Enrollment Period) to enroll in an exchange plan. You will need to upload a utility bill PDF or another document to the exchange with the new address.
Documents to confirm move:
https://www.healthcare.gov/help/prove-move/
2) You will have a "loss of coverage" SEP when COBRA expires. Just make sure the COBRA plan's provider network includes FL providers if you choose to wait until COBRA expires.
3) Since COBRA will expire after 1/1/19, you can opt to end COBRA on 12/31/18 and enroll in an exchange plan on 1/1/19 using the annual open enrollment period. Again, be sure the COBRA plan's provider network includes FL.
Deductibles and OOP carry over from group to COBRA but reset to $0 met if you change from COBRA to exchange plan mid-year.