OK, first: congratulations on losing a huge amount of weight. Your current weight is much healthier.
Second: the DD boobs were basically the result of putting on so much weight. You could regard B as your natural size, if you're at a healthy weight. Because you've lost weight they are probably a bit saggier than they would otherwise be - but I think you are far more worried about this than the guy would be.
In terms of firming them up, you could try exercises to improve the tone & size of your pecs, but I'm not guaranteeing miracle results.
I'm afraid if you are dead set on getting big, shapely boobs without putting on weight, your only other option is cosmetic surgery. If you think your breasts are a complete disaster (I'll have to take your word for this), you could perhaps try persuading your GP to refer you for cosmetic surgery on the NHS for psychological reasons - but I'm afraid you're not that likely to succeed (it's done very rarely). Private boobs jobs are not that cheap - but please don't get it done overseas to save money - you have very little control over the results you get, which are often quite unsightly and unrealistic, and there are lots of health risks from inadequate follow-up and poor professional regulation in some countries.
In the meantime, I wonder whether you could try hypnotherapy or books about self-esteem - what you need to realise is that loads of girls have worse problems with their looks than somewhat saggy boobs, and still manage to find decent-looking guys. 90% of this problem is in your mind.