The pics in the other post is really great! You have mentioned investing in a blazer, havn't you? A blazer and a skirt would add some extra dimension to your wardrobe. How do you feel about a denim skirt? To me that mixes both casual (sporty) and business, especially if you get a darker and saturated color, or go towards a gray scale.
Working on your business wardrobe, you could give it some time to adjust to your new job. Or if you are really patient, you could get more spring items on sale in july/august or make a plan and wait until next year (yes, maybe a bit boring, but I'm just thinking baby steps ;-))
Why would the top of the boots be hidden while standing? Do you have over-knee boots?
About black tights, I don't mind wearing black, even in summer, if you add other spring/summer elements. You could also try grey or charcoal which is a bit softer than solid black. Or maybe even midnight blue.
Do you want spring items right away, or could you do with just a dash of spring? Like a ring, bracelet, necklace or scarf ? I saw some really nice at Indiska the other day, but can't find it on their web site, just this ring: http://indiska.com/Accessoarer.....33347MULTI