Ha, ha, ha. Wish my mom had told me not to slouch as I have terrible posture. I don't see sloping shoulders, but if you say so. . . .You might want to check out Angie's tips for Pretty Pears to see if it resonates with you and what you finds works for your body. The other thing you may wish to do is check out her tips for ITs (Inverted Triangles) and AVOID those things. Look for tops that are structured (fitted) in the shoulder and or have shoulder detail like epaulets on military style jackets. Small shoulder pads work, too.
To get the most bang for your shopping buck: Make sure everything can be returned. I have found that even if something fits well and looks great in the store mirror, upon my return home I find that its proportions don't quite work with what I have or the colors are off with what I planned to wear with it. Don't settle. If something doesn't fit quite right, is scratchy, or whatever, you may not want to reach for it. A bargain is no bargain if you never wear it!
Note: I wrote you a long posting a couple of hours ago, and then inadvertently deleted the whole thing. Ugh!