I dont' think it will be that cold in Ukraine in March -April to need sheepskin inserts or fur-lined boots, or indeed thermal layers. Depending on when in March you go, and where in Ukraine (it's about the size of France, so different weather in, say, Odessa and Kiev), you are likely to have between +5 and +20C, so not that different from London weather now.
I would focus on wearing well-fitting suits and looking groomed. Women in Ukraine tend to overdress in a "bellla figura" style - too fashionable, quite a lot of make up, sometimes verging on tarty, especially in smaller towns. So what passes as normal office gear in the UK may come across as frumpy granny style or as if one just threw things on without thinking (sorry OP, I have no idea what your style is, but when I go to Kiev or Moscow I always make sure I look my smartest and most polished).
One thing to consider for your trip in March is footwear. While the temperature may be fairly warm and pleasant, there may still be a lot of puddles and slush in the street (which does not stop Ukrainian women from wearing splendid high-heeled boots...) So thick-soled ankle boots and apply a lot of protective cream.
Hope you enjoy your trip, it is truly a beautiful country with amazing people (and horrible government...).