As I'm still wearing guy clothes they usually get stretched within the first day or so. I've already moved down from L/XL to S/M but due to my shoulders the fabric will stretch somewhat giving that awful baggy appearance.

As for the tops I've tried out the sleeves will just go slightly up looking like cap-sleeves which is a big nono. Wearing 3/4 sleeves sure does the trick but I can't walk around in that 24/7, not mention when it's summer. Trying anything "sleeveless" (i.e kimono) will just hide my waist giving me a even broader view. The thing that bugs me the most is why they don't make regular sleeves like for ordinary (Mens) T's. The only ones I've found and tried out are unisex ones which are slightly cut by the waist, but even these are rare.

I have a Mesomorphic female type, hourglass-shaped but with broad shoulders. Dressing "properly" to hide these will only leave me with a Endomophic look and that makes it look even funnier. I basically have to dress like a box in order to hide the oh-so-obvious am I right?

Your thinking about things the wrong way, the same as any woman with broader shoulders and narrower hips, you need to dress to accentuate the bits you don't have rather than to hide the bits you do. You say you have an hourglass shape, so use it to your advantage. Things that tie in at the waist and then flare out at your hips will balance out your shoulders, in fact anything that accentuates an hour glass figure will make you look more feminine even if you don't necessarily have something flareing out at your hips. Plenty of women have broader shoulders than their hips so it's not really as much of a problem as it may seem, it's just a matter of thinking about clothing in terms of your body shape.

wear slimming tops and wear bottoms to accentuate your hips. tops with a soft, U-shaped neckline, soft flowy sleeves and a defined waist work wonders, especially if you use darker colored tops and lighter colored bottoms. anything that makes your hips look bigger will help. skirts that are bulky and ruffly as opposed to denim skirts.. tight pants in lighter colors.. things like that.

look up fashion tips for women with an inverted triangle body shape and you'll find a lot of great tips to accentuate the hips and soften the shoulders.

low neckline taking attenion away from the shoulders
dark clours help, aviod large prints. prints shold be in the lower areas

tops and jackets should be long, hanging details works wonders to give a more slender apperance