Hey, there!
Natively, it’s not currently possible to stack discount codes to offer both free shipping and discounted products. That said, I was able to find an existing feature request to have this added to your platform from other store owners who’ve requested the same thing. I’ve gone ahead and added your vote to this request to show our developers there is further interest in getting this added. Should this be something we’re able to launch, then we’ll make an announcement on our announcement page to keep everyone in the loop!
In terms of a workaround, you could offer a free shipping rate, while still offering a discount code at the checkout which would give the best of both worlds. That said, the shipping rate can only be set per country, and not per product which does throw a wrench into things if you’re hoping to limit free shipping to a specific product/collection.
Let me know if you have any other questions!