Do you think perhaps you could link to a site you have good experience with? I would love to get some backup pairs but I worry about the cost

As others have commented yes Glasses Direct are who I’ve used. They let you choose some frames to have sent to you to try on in a selection box. I did this the first time.

They require you to send your prescription (a photo is fine) before they make them, which makes me think they are being required to do that legally, or at least concerned they don’t want to get it wrong.

So this doesn’t turn into an advert for one company, I did notice that lots of other companies seem to offer a very similar service and they all seem to offer various guarantees regarding your happiness with the product, presumably because people are still wary of this way to buy glasses.

Another reason I’m slightly evangelistic about using these ‘online’ glasses services is that the high street opticians are obviously overpriced and I don’t think it’s right to make so much money unnecessarily from people who just want/need to see well - some of whom really struggle to afford the costs.

I've used https://www.glassesdirect.co.uk/ . The prescription was wrong, so they gave me a massive headache, but an optician measured the glasses and said they were made exactly to the incorrect prescription.

(The second optician was helpful, so I bought glasses from her. I'll use Glasses Direct for sunglasses and so on.)

My dad has had a good experience with Glasses Direct in the UK. They are not the cheapest online store, but they have been around for a long time. They also offer a home trial for some of their glasses (if you are in the UK)

https://www.glassesdirect.co.uk/

My problem with that is that my frames needed adjustment few times after I bought them(they felt fine in the shop, but after few days they felt a bit too tight). The retail shop I got them from corrected them for me for free, but had I bought them from an online store I don't know what I would have done.