Hi there lily.
I'm not the most confident person in the world either but I've become much less self-conscious in the bedroom over the last few years.
I'm also not a fan of the look of my lady bits either but having looked online at other ones I can see mine are perfectly normal and nothing to worry about. Bits in my mind are just not particularly attractive to look at whether male or female but to other people they look great.
A few years ago I decided that it was time that I discovered what all the fascination with sex was all about. My children were a little older so I wasn't so tired anymore and I had more time and energy to spare.
I read up online about different positions to try, discovered how to masturbate, found out what felt good and how to make myself orgasm and squirt!
We bought toys together from Lovehoney to try. A bullet, cock ring, blindfold, satin wrist tie and feather tickler to start with and experimented with them. We had lots of fun. The community there is great for advice and tips too.
You said that you don't like the outfits you have but what did you buy? I found a babydoll set very feminine, flattering, comfortable and pretty to wear. It covered my mum-tum area which is the bit where I have stretch marks too. If I am wearing a bra and knickers set or a basque then a sheer or lace robe over the top makes me feel less exposed and self-conscious or a crotchless bodystocking is great for disguising my lumps and bumps and allows easy access if needed.
Try on your outfits that you have or get some new ones and wear them when you are all alone to get used to having them on. You could do your hair and make-up, accessorise with some jewellery a masquerade style mask, heels or boots. Take some pics on your phone and if you feel brave send him one with a flirty message. It doesn't have to be a full length pic. It could be a little flash of your favourite bit/s like your bum, legs or neck with a hint of cleavage to tease. Look for poses online that flatter. Play around with filters, colour, black and white and cropping and rotating the pictures. It amazed me how good and professional that they can actually look! It can be a great confidence booster too.
The "perfect" pictures we see all the time in the media are all clever angles, lighting and flattering poses and the models themselves admit that they don't look that good all the time and that out of dozens of photos there is only a few that look right.
I used to be a lights out under the cover of darkness type girl too but now I can relax and just enjoy us being naked together. I don't scrutinise my DH or look for flaws when we are together which I'm sure your DP doesn't do either. I just enjoy all the sensations and the warmth and softness of his skin and let go. It took me a while to get there but I find that I'm much more relaxed about sex and enjoy it much more now.
I read a lot of erotica which got me feeling sexy and watched some woman friendly porn online. Which got me used to seeing other people naked and realised that beauty comes in all shapes and sizes and that a little confidence is very sexy. It was great to see how powerful and happy these women looked. The site I used to look at was Lady Cheeky (but it got a bit glitchy) and they had really nice arty photos, gifs and short clips to suit all tastes.
Initiating is hard but I usually find that with us we are quite touchy-feely (kisses, hugs, hand-holding) all the time on a daily basis and that when we are alone passionate kissing usually naturally leads to other things anyway without either of us making the first move.
Things like Bio-oil are supposed to help improve the appearance of stretchmarks and they do fade a little naturally over time. I find that a gentle body scrub and body butter or lotion makes my skin look much better and feel lovely and soft.
Hope some of this helps. Good luck x