You'll need at least the Essentials plan for Thinkific to make a course or bundle of courses a subscription payment plan.
If you want to give students a year of the subscription when they buy the course, you'll need to make a coupon (also available on Essentials).
Here's the strategy:
Create a course or a course bundle and give it the subscription pricing.
You'll need a course with a fixed price and anyone who buys the course gets a free amount of time off the subscription so make a coupon 100% off the first X months of the subscription and then send it to people who are newly enrolled in that course only.
You can automate this by setting up a direct integration with an email service provider if you want to use ConvertKit, Aweber, or Mailchimp. Otherwise, you'll need to use Zapier, a service that that will connect Thinkific to another program.
Then, in that integration, make sure each new student of your fixed price course that nets someone free time off of the subscription is added to a mailing list with an autoresponder set up to shoot them an email with the coupon for time off the subscription you set up earlier.
WHEW! How's that sound?