I work in this area and our clients feel that the personal appearance of their staff has become more and more important. You might think it's nonsense but it's not about what you think, if you care about your job and want to keep it what your employers thinks that matters.
Obv I don't know anything about your company or role so I'm just giving general advice here. PM me if you need more help (no charge for a fellow MNer
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You don't need to think about losing weight but looking polished is essential. You can keep your clothes ironed, shoes polished, nails neat and even and hair clean and tidy yourself. That shouldn't cost you an extra penny. Body odour absolutely has to be controlled. I'm sure you have already heard plenty about not wearing man made fibres against your skin etc etc.
There's also a bunch of other behavoural psychology behind it but in a nutshell -
Empathy. Look like your boss / desired clients. If you are good at your job looking similar to them just cements their positive feelings about you. If they are looking at streamlining their workforce this can be as useful as working longer hours etc etc. And by 'look like them' I don't mean male, blonde, muscly etc, I mean if they wear smart conservative clothes copy that.
Validity - look like you belong. If you look the part people automatically assume you are capable. Helpful if senior managers who don't know much about you are making decisions about your future.
Individuality - this bit is harder. You need to fit in but not so much that you just look like a worker drone and get forgotten about. You want to be one of the first people that are remembered when senior management are thinking about your team. People that look smart get remembered.
And a final point before I get flamed. This is just about work, try not to think of it as some sort of question about your 'style', 'attractiveness' or 'fashionability'. It's completely different.
Good luck OP.