The best way to go about it is to simply enable airplane mode (which works properly on GrapheneOS) when possible and to use Wi-Fi. It’s very difficult for most people to never have access to data so I don’t think no SIM is a very practical approach. Just turn on data when you need it, but ideally not when on the move is my advice.
You can buy a non-KYC’d SIM as long as you recognise that still has significant limitations. As soon as you use it at home / at work it’s trivial to link to you, still marginally better than a KYC’d SIM though.
Read more in this topic: Mobile phone location tracking via cell towers - 4G vs 5G
PS: Let’s continue discussion of cellular tracking there if you have further questions.