This seems like a pretty significant non sequitur, and in fact is the opposite of my view (and I, like you, was already quite slim even ad lib): as a guy who already has little muscle and thin bones, you are unfortunately at more risk than an average person per kilo of mass lost ...
But I have little muscle and low bone density, so I think I can start CR and lose weight without too much to worry about.
Lots of people, when young, have 'subnormal' BMIs (though it's becoming rarer all the time...). That doesn't mean they're CRed. As I've noted before, there's no such thing as being "naturally" calorie restricted:
reading this I would suspect, that you are already doing CR for some time; 60 kg at 185 cm is certainly not the "normal" range for non-CRON people.
No one is 'naturally CRed' (cf the studies in lean vs overweight-prone strains of mice). Wherever you start from, you need to cut Calories. That's probably a big part of the reason why the epidemiology fails to find a longevity benefit to low BMI: people with low BMI aren't on CR. If you're already skinny, you just need to get skinnier. ...Some skinnier people are eating tons but getting exercise, or have pre-existing illnesses or malabsorption issues, or what have you. ...
[U]nfortunately, as I've said before, determining exactly a given person's "% CR" as a translation of the equivalent rodent phenomenon is impossible in free-living, genetically unique humans, at a minimum, human CR should operationally be defined as restricting down from the level of intake that supports the lower of (a) your early-adult "setpoint" weight, and (if that 'setpoint' was already overweight) (b) a 'healthy' anthropometry, based on % body fat, waist-to-hip ratio, and (ideally) visceral adiposity. (Unless you've got a colony of a hundred or so identical twins that you can lock up and force to eat the same ad libitum diet and get the same amount of exercise for a decade or so ...).