If you are only listing 2-3 items a week, and each listing costs you 18p incl. VAT to add, you’re only paying just over £28 in listing fees. Is the Plus account still £45 for a year?
Not sure what else you get out of Plus now to make it worth the extra. The constant relisting to be seen isn’t necessary anymore because of the improved search, so unlimited relisting that you get with Plus isn’t a selling point now.
I think Plus is only really useful for people who have a high volume of items, like supplies sellers. But there may be some benefit that I’m missing, and I’m sure a Plus seller will be along to add it if there is
Edit - Just looked at your shop to see if your prices are good. I’m afraid I can’t help with jewellery. As long as you’re covering your supplies, a bit for your time (if you want) and a bit more for the charity (or this including your time money if that’s how you’re working), then you’ll have found the right price. If things start selling well you can always top your prices up a bit.