Help please! - how to list multi-buy discount items for multiple designs?

Hello lovely peeps (who are hopefully for technologically savvy than me!!!)

Can you please help me or give me some advice? I sell funny and inspirational magnets (£1.75 each) and have over 160 designs available. I want to offer a multi-buy discount (any 5 for £8) but can’t seem to find an efficient way to do this.

My options are
a) To let people click on 5 individual items, put them in their basket, and then add a discount code at checkout. The problem with this, is how to give them the discount code - unless I go into every single individual listing and write it in there (which would take forever). Also, people don’t always read the text, so might not realise it’s available.

b) To do a separate listing for a multi-buy (which is what I have at the moment - see below) which solves the problem of pricing, but they can’t specify which items they want. At the moment, they just free type them into a message, but the problem with this is that some items have similar names and themes, so it would be very easy to make a mistake and send them a wrong order.

c) Ideally, I’d just like to have a listing in the magnets category of my shop that says - “Enter discount code: MULTIBUY at checkout”, so they can just shop as normal and apply it at checkout, but when I tried to do this, FOLKSY says "you need to put a minimum sale price on a listing of 20p)

Is there a way to do option b but actually be able to click on the items in my shop so I know what they want? Or… is there another way to do it? If anyone offers anything similar, can you please send me a link so I can look at your listing?

As alway, any tips or advice greatly appreciate.

This is what I do for mine - Card Pack Mix and Match - any 5 greeting cards - Folksy

Have a separate listing with a text required variation, and then put a code on each card listing so they don’t have to type out full titles or hope they call something the same thing I do.
I have a lot less cards than you have magnets so I can imagine it could still be quite a bit of work giving codes to everything, but an option to consider.

The issue that I can see with a discount code is that they are a % off and would apply to all items in their basket (from your shop) so if they were buying some of your eg hair grips as well as the magnets they would get a discount on those as well.
If you give each item a product code at the end of the title and then have a required text box as a variation on the set of 5 listing they would need to add the product codes before they check out. But even that isn’t ideal as they might not specify 5 product codes and you would need to look up which code goes with which item when picking the order.

This is my solution. I tell them to let me know which ones they want by using the ‘notes to seller’ box at checkout, and that if they leave it blank they will get a ‘lucky dip’ of my choice.