I agree that a different shampoo can make a difference- mine definitely feels softer with some shampoos than others. I don't do much with my hair - I swim quite a bit, and I never blow dry it, so it needs to be something whuch doesn't need much styling. For me. I'm not you. A good cut can make a difference, and I do keep mine neatly trimmed. I wouldn’t get mine dyed, because that wouldn’t feel like me, and I certainly couldn't be bothered with maintaining it - but if dyeing it would help you, then talk to a stylist. A change of colour can make you feel quite differently about yourself. I'd start with a good cut, though.
I don't wear make up, but I do use moisturiser, because my skin gets tight and dry otherwise (I am older than you - perimenopause is a factor for me.) I need something that sinks in easily and doesn't make my face feel fiery or sting. If you do wear make up, then I think you need to feel comfortable underneath it, so I think moisturiser etc is important, and there will be something which will suit you and your skin.
Posture also helps - standing up straight, shoulders back. It will make you look more c than if you hunch over, trying to hide yourself, which is a more instinctive, self-protective way to be when you feel down. Physically standing up straight, or sitting up straight takes more physical space, around can trick your body into feeling more confident- literally fake it till you make it.
Clothes that make you feel good can help - think about the colour and fabric. A colour that suits you will make you look better, but I find colour affects my mood, too, so I'm in red trousers just now. I'm fussy about the fabrics I wear, so my wardrobe is largely cotton and silk, not many man-made fibres except gymwear. Again, that's me, not you, but clothes you feel comfortable in will help. Well cut clothes which fit well are good, too.
And you know, fairly healthy diet, regular exercise, good sleep - annoyingly, it does all help.
But it doesn't matter what you know rationally because it's about how you feel emotionally about yourself. That can block you from believing your husband. If you can't get past thst, maybe counselling will help.
I do agree with vitamins though. I'm currently on ferrous sulphate for anaemia, and I just noticed this morning I've only been taking half the daily dose prescribed, so no wonder I'm still losing hair... oops.