Take this with a pinch of salt as I haven’t got my head around water science either but as an interim solution, I’ve always just used bottled. Waitrose Lockhills is 70p for 2l and I use two a week, so about a fiver a month. I typically order 3 packs with our grocery shop and then not worry about it for 3 months.
The environmental aspect bothers me a bit but the bottle and cap are recyclable.
LM actually recommend using bottled (Acqua Panna). I suspect there’s a business relationship behind that as well as functional, but I’m sure they wouldn’t recommend it if it led to scores of angry LM customers with scaled-up machines.
The consensus seems to be that bottled water will still scale but the question I have is how long will that scale take to become a problem that needs descaling if using exclusively Lockhills/Volvic? If it’s 10 years+, then I’m ok with that. But if it’s likely to cause issues after say 18-months then I’ll reconsider RO.