At the moment, every time I want to access my server, I have to turn off my VPN so I can turn on tailscale.

Yes, mobile devices typically cannot run two VPNs at once. There are two issues here, when at home and when out on other networks.

At home, the solution is not to round-trip out to your VPN provider and then back into your network via the public Internet using your domain. Unfortunately. That creates a huge latency and bandwidth penalty when you are physically at home and unnecessary complexity.

Instead, if you must use your VPN service while at home, you need to find the split tunnel settings to allow your phone to access the local network while connected to the VPN service. They usually hide that setting because it opens up the security of said services and allows some leaks, but it should be there.

When out on other networks, it gets harder. If you get creative with networking, you could connect a computer to your commercial VPN service and have all your tailnet devices use it as an exit node, which has the nice benefit of paying the VPN service for “one device” and using as many as you want, but is dependent on your home network speed and a PITA to set up.

Tailscale does integrate with one VPN provider so you can use one app for both tasks, but it may not be the provider you want. I don’t know If their direct competitors do the same, maybe shop around a bit. One VPN app for both use cases is what you want, not two different VPN apps.

Finally, if none of the above works for you, then yes, you are back to accessing your self-hosted services via the public internet and your domain name while travelling and using your commercial VPN. You will have to secure the service, and that will take some learning to do safely. That will be a journey and not something you want to just throw together quickly. You might be able to restrict incoming connections to just your commercial VPN IP address range (in addition to all of the other proper config required) to further reduce the attack surface. Sorry, that is a bit of bad news.