If not Phoenix, Breeze and Blixt, why not use a hosted lightning node like https://voltage.cloud and connect to/manage it with your mobile wallet? This should be sufficient for spending money while remaining sovereign and independent of a proprietary service. The majority of your coin should be in an offline wallet anyway.

For larger on-chain payments I'd probably go with a node on a laptop. The node doesn't need to be running 24/7. Just re-sync whenever you want to make a payment. You could do that with public WiFi + Tor at a cafe or something like that.

For day-to-day payments (i.e. Lightning), what's wrong with the non-custodial mobile wallets like Phoenix, Breez and Blixt?

How to use LN for your personal use, practical solutions: https://darthcoin.substack.com/p/private-lightning-nodes

Buy an additional smartphone with a SD slot + 1 TB Micro SD card, then How to install full node on a smartphone.

Well, depending on network speeds, a full node can handle dropping on and off the network quite regularly.

For LN, I'm not sure what the best solution would be. This article gives a good review of several common LN wallets and how well they worked with bad internet.

You might also want to look at how the LNURLPoS works, as it is capable of functioning without an internet connection, although it does this by using the phone's connection and not that of the PoS, so it might not be useful.

Maybe, depending on what prices you can get for data, rig up a battery powered LN node with mobile data that then uses a watchtower to account for times you lose service.

It you have someone that you trust enough, though, I would reccomend just storing it at their home.