How about doing the knee boot with a sharp little A line on the knee skirt (maybe with an inverted front pleat) paired with a soft sweater or sweater/sweatshirt and a tank in toning or contrasting colour peeping from beneath? Add a blazer or jacket, a scarf and you have a look that would do for work, home and play. Look for kilt type skirts in checks or soft woollen fabrics. You can get that rosie look with a skirt by looking at her layered top half-jacket and tank or shirt and jacket with a scarf and a pair of winter sunglasses for bright days. This look is what i mean and works with boots and ankle boots plus choose the colours you like as separates. This is a sharply cut skirt, the style I am referring to.
You don't have to wear this pant style if you prefer jeans but this look from Oui has the little boucle knitted cardi jacket with a T shirt that is very modern but also classic. it won't date too much and you can wear whatever shoe you like with it. The same here in that it is all black but the belt makes so much difference. Try on some different shaped pants but make sure they are in a wool blend fabric so they hang well. Department store staff are your friend here in trying on styles and make sure you try them on with the heels you plan to wear them with.
If you look at this pin, you can see how layering different lengths of chains can modern up a simple shirt. Imagine this shirt worn with a dark denim jean or navy,grey,burgundy or brown cords and a jacket will give you that Rosie look too.
I would splash out on a really good pair of jeans and also try jean cut cord trousers in a skinny or straight cut. Jewel colours such as dark burgundy, dark purple or chestnut brown worn as jeans or cords would look good. My way to dress them up is to buy a good blazer/suit style jacket in black, grey or navy and wear this with them. To go out you can put a sparkly top on over jeans with heeled ankle boots and with the jacket. This is the jacket/jean/shirt/sweater look that is never frumpy.
A good hair cut can help too as can lessons from a stylist in how to blowdry well.
This pin shows how muted classic colours work at a neckline. Again, wear this style with a pretty skirt or a an a line skirt or even a gathered flared skirt. Or with jeans and a heeled boot.
How to wear black and cream here. You can choose a flippy black skirt worn with a cream top. Pair them with knee boots or ankle boots and thick tights and see how black is not boring. Navy and cream works well. A lot of it is in the fabrics you choose. Contrast a thick wool sweater or cotton sweatshirt with a flippy skirt and thick tights for warmth.
Here is a cool everyday casual look. Imagine this sweater in red/purple/black as well as breton stripe. Pair it with your trousers and choose a cool belt and bag. Accessorize has great clutches that I promise will make you feel different when you carry one.
Tops like this Atterley Rd one will modern up any jean or skirt worn with. Again, wear under a blazer. Look for 'hybrid' sweater/sweatshirts like this to wear. Instantly modern. Uniqlo make good sweatshirts and T shirts in good deep colours.