I'm a few years younger than you, gentleshores, and still working. I usually wear full-length, tailored trousers (wide or straight) or a midi skirt for work with slim fitting tops. I dress for comfort at home, so that means really comfy leggings and long, loose tops and if I'm out at the weekend it's usually jeans, tops and blazers or loose, knee length dresses and boots with tights.
I admire people of all ages who use accessories well to update their look and older people who seem to have the knack of getting the casual look right. Like you, I wish I could wear more casual clothes and not look messy. I always feel as though I have to dress a bit more formally than I'd like, just to avoid looking untidy.
Even though I'm still slim, as I've aged, I find that tighter clothes don't suit me and they're too uncomfortable. I'm finding that I need more things I can move around in freely. I spend a bit more on outerwear, as I think a good quality coat or jacket is a good starting point for whatever else you need for your wardrobe.
I also try to make an effort to look a bit more polished these days. For me that means smoother hair, light makeup, taking care of my nails (basic manicure) and clean, better quality footwear. The dishevelled look only suited me when I was young.