If you're looking to shake up your email provider in the wake of this, I highly recommend getting a custom domain name, whatever provider you choose. Cloudflare sells domains at cost. Get a not-embarrasing .com of your own, and then you can move email providers in future without losing continuity. Proton allows exporting .eml files, which you can then import into your next provider. Or just keep in cold storage and declare email bankruptcy. Once you have a custom domain, you can use unique emails for all your services by setting up a catchall address. This will at least impede credential stuffing attacks, and let you know who sold/leaked your address if you do get spam.
I personally left Proton a month or so ago after the last bit of drama, in part out of principle, but also because their offering is just really expensive for my use case: I just want email, on a budget, with reasonable privacy. Plus I was tired of not having IMAP support and being locked into their clients. Moved to a Zoho business account (for now) and have been happy for the $12/yr. I already had a domain name, but they typically run <$20/year too.
Get an embarrassing domain, then give that one out to all the shitty stores that ask you for an email. Bonus points if it will make people extremely uncomfortable.
You don't have to do anything else with the domain, it'll work fine for email only.
You could add it to Proton, take your time to migrate all your accounts, then dip. Or you could just go straight to a new provider with the domain, and take your time transitioning accounts to the custom domain over time that way. Assuming Proton's free offering is sufficient, you can always keep it around and set up forwarding to your custom domain.
Regarding domain name setup itself, Proton should provide steps for how to do it correctly, but I found them to be a bit fiddly (might have improved, this was a few years ago) - when I moved to Zoho I found it really easier. If you're using Cloudflare for the domain registration, Zoho can basically do it all automatically (click a few links link and accept the proposed changes).