[deleted] the mobile network is inherently a tracking network, so no matter what provider you use, it will hardly be a private experience. Here's a good summary on why GrapheneOS is treating every cellular network as hostile.
All major providers have been caught selling your location data (to various degrees depending on your jurisdiction), and the small ones just rent from the larger ones, so it's at best an added privacy layer.
That all being said, your best bet is to use a foreign provider with the eSIM always in roaming mode that allows you to order and pay anonymously. You'll still be identifiable without very careful OPSEC, and you still share a lot of data that threat actors can use for profiling. I only know of silent.link as such provider, and they will only help you as long as you make sure to never link your data (e.g. your location) to your real life identity.
If possible, don't use a SIM or eSIM at all, but VOIP number providers such as jmp.chat. If you require internet on the road, maybe get a mobile router such as the Gl.iNet Mudi 2 that you use with an anonymous physical SIM card.
But maybe most importantly: Make sure to have a good threat model so you know what you actually need to protect and from whom. Fighting for cellular privacy is an uphill battle, and you might achieve much more when focusing that energy elsewhere. Just make sure you have a clear set of goals to align your strategies with.