Button on product page for single item or a pair

[Feemish]

I have jewellery items which people often buy in pairs but some people want to buy as a single item.
I currently have a quantity selector on the product page with a message saying 
'price is for a single item not a pair' and people mostly understand and click quantity to 2 if they want a pair.
However ever now and then someone doesnt read properly and clicks one item and then complains when it arrives saying they thought they were getting a pair.

I have noticed other shopify stores have this set up;

clicking 'buy single' adds one pc to the cart
clicking 'buy pair' adds two pcs to the cart
Importantly... they both take stock from the same SKU inventory. 

(I know I can add another variant choice (single or pair) but this requires seperate inventory for each which will make things very complicated and unworkable)

Can anyone tell me how to do this?


NOTE 
On items that never come in pairs the same store has this on product pages.. So I expect there is a product page template being used for the single/pairs pages.

Thanks!

[Feemish]

Hi Daniel,
This sounds perfect. I'd very much appreciate some help on how to set this up!

[Feemish]

Thanks... but what is that slightly dodgy looking .csv file? 😅

[Feemish]

@Danieljohn543  Hello? Your comment on how to solve this issue seems to have been deleted?

[Guleria]

Hello @Feemish ,

You need to use line item/custom fields to achieve it.
Here is a UI genrator which can give you an idea  https://ui-elements-generator.myshopify.com/pages/line-item-property 

You can use radio field and design it accordingly.

Regards
Guleria

[Feemish]

I had a look at the link but sadly i'm non the wiser..