I think I found/decided on a solution. Based on how I was leaning and with help from all the responses and particularly @Henry 's response.
I will try Proton Free on my Mac (with Mullvad browser), and I somehow apparently also have NextDNS working/running on my Mac. I got 100% with the d3ward ad blocker! iCloud Private Relay will be my backup plan.
On iPhone I think I will try Windscribe free. With iCloud Private Relay and custom DNS as a backup. Proton Free was giving me horrible results (like 2-38%!) on the d3ward ad blocker in Firefox and Safari for some reason. With two free servers I tried anyway. Not sure what is going on. Maybe less ad blocking on the free servers? Need to test more.
Update: Currently decided to use iCloud Private Relay and NextDNS on iPad.
Not ideal, for me, to have three separate setups on three devices. Ideally I want just one solution on all three devices, like Mullvad. But that is the compromise with free. I will get Mullvad as soon as I can afford it.