I've been thinking about this some more, Jane, and am just writing things down randomly here as they came to me, so sorry if this is incoherent;-)
First of all: you have an amazing wardrobe, and are already doing a fantastic job of dressing amazingly well for work!!
- I could really see you rock patterned hosiery whenever you need a change from your opaques. I know you're a bit reluctant about it, but maybe a good way to ease into it is only wearing patterned hosiery with on-the-knee/just-above-the-knee skirts and dresses and pairing them with knee-high boots in the beginning (or mid-calf culottes and booties)? That way only a small part of the hose is exposed, but it's still enough to add a little extra textural and visual interest. (Keeping things tonal will help too, e.g. navy dress with navy hosiery and tall black boots, or burgundy skirt with burgundy hose and taupe or grey tall boots, etc.)
- l love Angie's idea of tonal dressing too, that always looks sophisticated and professional. As far as adding colour is concerned (if you are interested in that to begin with, it's not a must;-): no need to do brights or "loud" colours if that's not your thing, and no need to do it head to toe. Adding a touch of burgundy, or olive or dark green, or whichever colour appeals to you could be a nice way to switch things up when you want a change.
- Would a leather or suede skirt or even leather trousers work in your line of work, Jane? If you keep the rest of the outfit very Modern Classic, it could be a great way to add soft edge to a look.
And how about dressy jackets that are not blazers?
- Playing with pattern even more than you are already doing. I love the pinstripe suit in your photo, and you have a knack for finding beautiful scarves and pattern mixing them with the rest of your outfit.
- Something else that you are already doing, and that makes every outfit look more special and interesting: Wearing one item in each outfit with an interesting design detail (sleeve or collar that is a bit different, an interesting pattern or touch of colour, the cut of a dress or skirt, an asymmetrical detail, a gorgeous scarf or piece of jewellery, patterned hosiery, a shoe with an interesting heel or buckle, a two-toned cardigan, coat with contrast piping, a peplum style top or skirt, pussy bow blouse, built-in layers, lace or other textural interests, decorative buttons, a statement belt..).
I'm adding some items below just to illustrate what I mean. Ignore the (bright) colours if they don't feel like you, it's just to show silhouettes, details and general ideas:-)