Single payer is _ludicrously_ more efficient at buying everyone healthcare because it can buy in bulk and it can be hard-headed about cost-benefit decisions.
When it's your baby, the idea of paying $50 000 for a 1% chance of not needing to amputate her arm is a snap - of course you'll pay. But the single payer says hold on, that means we're paying an average of $5M per arm saved, arms aren't worth $5M, our tax payers say they're not willing to give us more than $2M per arm, offer the treatment for $20 000 or no deal.
Making people invest in their healthcare _can_ help with some personal care decisions, like whether to take exercise, eat better, maybe give up smoking, people who feel like it costs them money when they're sick are a little more careful in some ways. But a LOT of healthcare spending is unpredictable, so isn't affected by this at all, including very expensive urgent and emergency care. Overall single payer wins out in terms of both how much you spend and outcomes.
A UBI does leave open the question of what you do with the small handful of people studies suggest will not spend their UBI wisely. If you give everybody $300 per week, 999 out of 1000 of them will spend it mostly on food, and shelter, and other useful things. Their priorities might not be my priorities maybe they eat a Big Mac instead of making a healthy salad, but they are behaving wisely by their own standards. But one person out of a thousand will spend it all on lottery tickets, booze or heroin, and then what do we do about that? Leave them to die? Really?