"Flattering" depends entirely on the observer's viewpoint, highly subjective. It also depends on the body underneath. For example a size 8 person might want a fuller (fatter) bum, while a size 18 might want a smaller bum. Size 12 is quite average, so I don't know which way to go flattering.
When you say "not too short", can you specify a length or range of suitable lengths?
I believe that patterns and large textures tend to be unflattering on most people, so personally, I would choose a solid colour, or a simple camouflage.
As it is a hot summer, I would choose 100% cotton or linen.
Are they for casual, formal, party, beach, street, sports, or work, etc? This determines the style more.
Do you like buttons, zips, pockets, straps, belt, etc.?
Do you want holes, rips, nets or non-windowed?
Do you want a low or high waist? Belly button seen or covered up? If seen, how far up is your belly button between your groin and your underbreasts? I ask because a navel higher than halfway might suit a higher waistline.
do you like frills? Lace? Bows? I would avoid bows.
Do you like flared, straight or tapered?
Pleats vs non pleats?
What colour top would you be likely to wear with it?
/how would you describe your thighs? (Skinny, average, large, toned, flabby, cellulited, spotty, hairy, scarred?)
Do you have any body confidence issues regarding your legs, hips, butt, groin, stomach, back, etc?
Are there any example styles you like? What are they?
Do you want a raised butt (e.g. scrunch butt).
If you can answer all these questions for yourself, then searching will be much easier.