How to add variant without increasing stock quantity?

[chicario]

Note: newbie with an unpublished store.

I have an original painting as the base product. I want a customer to be able to buy it either framed ($120) or unframed ($100).

What I tried:

1. Added painting as Product

2. Adding variant ("Framed or Unframed?")

3. Adding two options - both with a Quantity of "1": Framed ($100), Unframed ($120)

This allows a user to add both the Framed and Unframed product to their shopping cart - which I cannot fulfill b/c there is only 1 copy of the original painting. 

Is it required to use a cross/upsell app in the above? 

[marcoswata]

You can use an app that allows you to offer the frame as an "add-on" (with the frame being a product at $20 in the backend). That way your stock is still 1, but you give the option to add a frame or not.

There are lots of options. This one is free.

[Cosmichealing]

what app do you recommend?