I should have said that, when I was at my lowest weight of 7 stone 12 lbs, I couldn't keep to it without effort and great care in what I ate. It wasn't realistic as a long-term proposition. An extra half stone may be, if I can ever get there.
I'm still uncomfortably aware that I'm sounding like a smug git before I start. There's such a wide range of what is a 'healthy' weight. I've got a couple of friends who are very slim and about my age - a couple of years older, perhaps - but actually they have gone past the stage of elegant slenderness and look a bit too thin and drawn. Other people, just as thin, look fine. And weight isn't everything - it's how you feel that matters. I think we do know what size we 'should' be, and it may be bigger or smaller than what the books say (obviously, I'm not talking about someone with an eating disorder) and is best, in the long term, governed by what we can stick to with a normal, but good, diet.
In my case, it's my shoulders that govern what size I should be. If I wear a tailored jacket or coat any bigger than size 12, I gain a pin-head. Last time I bought a suit, I had to get a 14 skirt and a 12 jacket, even though I could hardly do the jacket up, because the rather short and boxy jacket looked absurd in the larger size. "Hmm" said the assistant. "D'you think you'll want to do the buttons up?" We agreed that it was better to leave it open and look better than do anything silly like try to keep warm. A 10 is better again for my proportions, but that's a year off yet.