Signup form that adds Product to cart then takes you Checkout when clicking Submit

Hi All, Fairly new to Wix but have lots of Shopify experience.

I have a fairly basic Wix signup form I created which registers someone for a “Membership” and captures name, address, DOB etc.

As part of the Membership signup they also need to pay the membership fee. I have created a Product for the Membership fee. This product needs to automatically be added to the Cart as part of signup if possible.

There are also two other Products they need to choose from using a simple tick box and then that chosen product also needs to be added to the Cart as part of the signup.

So the workflow is as follows:

User fills in personal details for Membership
User ticks a box to choose an additional product (required)
User clicks Submit
Submit then sends them to Checkout where they will see a Membership product and the additionally chosen product.
User Pays

I don’t mind this happening as a few steps such as:
Step 1 - User details registers
Step 2 - User redirected to page listing product that they manually choose
Step 3 - User is sent to Checkout where they pay.