[corobo]

I recently came across fly.io (possibly on HN) which looks like it may help here, at least in the interim while you're a small startup. To note they do it for you similar to how Cloudflare would do it - you route your site through them - so it may not be what you're looking for.

https://fly.io/mix/custom-hostnames/

No affiliation on my part, the service has just ticked enough "ooh" boxes I'm intrigued and am looking at using them for a project or two

[stevoski]

I briefly checked out fly.io as a solution for this. It worked brilliantly.

I chose not to use fly.io though, because I was ultimately putting control of the DNS settings for all of my SaaS's custom domains in their hands.

[corobo]

The way I was going to do it personally was have customers point to a domain I control which then CNAMEs to the DNS record fly.io provides me. Not that I don't trust them or anything, but because I don't trust anyone completely :P In serious it was more to avoid any brand confusion.

At least that way I could in the worst case scenario cobble something together that replaces it in the event of a sunset or the likes