Adding another shipping option to local delivery and making it specific to just a few products

[WendyC]

About to launch my first Shopify store and am hoping someone can help me with the following shipping related question.  We are a flower eCommerce only store (ie we do not have a bricks n mortar store).

We will offer 2 product types:

1. every day flowers
2. flower subscriptions

We only offer local delivery to a handful of postcodes in Sydney (Australia). For everyday flowers we have a flat fee delivery and we have set this up and it works fine.

For flower subscriptions the delivery is included in the cost of the product.

How do we set this up in Shopify in such a way that:

in the checkout, the customer only sees the free shipping option on the subscription flowers (but not when they are ordering non subscription flowers).

I have tried to set up a custom shipping profile but this has the limitation of not being able to restrict the delivery to just a few local post codes. 

Is there a way to achieve this within Shopify without having to purchase yet another plugin?

Thank you in advance for your help.