When is it time for a cold wallet? Which one to choose?

As the bear market continues, I’m planning on expanding my holdings by around 100% gradually. This would bring me over the milestone of 0.1BTC. At this point I’m considering a cold wallet, I have a couple questions:

1. At what point would you suggest that buying a cold wallet is worth it? 0.1BTC, or more, perhaps less?

2. Since I don’t per se need iOS compatibility I was looking at trezor safe 3 or a ledger nano s plus. I’ve seen a ton of reviews but apart from the fact that one is open source and the other isn’t i don’t see many differences: which one is better?

Thanks :)