Your second "must have item" is a dark skirt. It should be made of a heavyweight fabric, preferably wool or one of its many imitators and/or blends. "Dark" means: darkest green (deep forest or pine), darkest blue (navy or midnight), chocolate brown, charcoal grey or black. It does *not* mean blood red, even the deepest of blood reds - although that might be an excellent second skirt in your wardrobe if blood red is a color that suits you.
(You may substitute "slacks" for skirt here, if you really really must. However, a skirt is a touch more formal and a touch more festive).
Again, the skirt must be impeccable in taste, in fit, and in repair. No dropped hems, loose threads, or pulling waistbands please. (I am *so* guilty of this).
I'm going to surprise you a bit and say that a long full skirt is not appropriate for this item -even though I am all about the long, full skirt for daily wear. Why not? Because a long full skirt currently reads as very feminine and festive, and you want this skirt to convey a certain seriousness. (You can offset the serious with accessories if you need to, but that's another story). You may certainly have a bit of style to this skirt, but you don't want it to be "of the moment" - you want to wear this for years, not a season.
A pencil skirt is a *great* choice for this item, and is what I'll be refashioning my long, full green skirt into. A long straight skirt is acceptable, as is a plain knee length skirt. Anything more than 1" above the knee isn't going to play this game - 2" if you have long long legs and it will look like 1" on normal humans. ;) Try to stay away from fullness when choosing this skirt. Again, a pleated skirt or an A-line would be a great second choice if you need something else in this vein. (I'm saying this as someone who almost never wears a fitted skirt).
You can play with texture again if you like, but make it subtle. Plain is *fine* for this skirt. Quality fabrics will show themselves to great advantage, so if you're making a decision about budgeting, this is where you should think hard about putting a little extra.
If you don't look well in white, I'd steer clear of a black skirt - go for one of the more subtle dark colors and let it warm up the white blouse a bit for you.
You will be pairing this skirt with your white blouse for your most formal occasions, and with more festive blouses or sweaters or... for less formal occasions. Although the life of a housewife lends itself to more easily cleanable fabrics, having this in the closet is a lifesaver. Do make sure it continues to fit! That's the worst thing, reaching for your "do not fail" item and finding it won't button or has an inch of extra room in the waist. You also want to take care of any cleaning or mending immediately - again, you don't want to reach for this skirt an hour before your court date only to find that it's a mess.