We've been trying to do the same. As a non-profit religious organization, recurring donations are very common. All we've been asking for is a check box that allows the donor to designate a recurring contribution. We use Stripe for payment processing, and while they enable recurring payments, it is only for existing donors through subscriptions. Therefore, we've hit a wall trying to add this feature seamlessly. You can set up a form for donors to choose a recurring donation amount. You'll need to go to Stripe and add thier email to a subscription and provide instructions to them on submitting a request to remove their recurring donation, which involves you manually removing their email from the subscription.
In the meantime, we offer our donors two ways to give—Squarespace (via Stripe) for one-time payments and PayPal. Which easily allows recurring payments without maintaining subscriptions, and donors can stop the recurring payment in their PayPal account themselves.