Please suggest beach cover ups over a skirt style on piece swimwear

Transparent kaftan will enhance the plump. i guess cotton will look better.. but if you have not decided then go for a trial and decide accordingly..

 

A few questions, before suggesting an option:
1-How long is the skirt of the swimsuit bottom? Thigh length or longer?
2- What kind of neckline on the suit-round, square, v-neck, sweetheart or something other? How deep is the neckline and how deep is the back neckline-is it a halter neck or one with the two shoulder straps, and how wide are the straps?
3- What color is the suit? And do you mind the suit showing through the coverup, or can the suit be viewed as a short dress?
4- Is the cover up for decency or to prevent tanning?

 

If the swimsuit has a long enough skirt, so it actually looks like a dress, like this one:
For decency, or to go into shops/restaurants, I'd go with a long, lightweight button up shirt tied at the waist in a contrasting color.
If the cover up is simply to prevent tanning, then a long sleeved lightweight cotton button up shirt (so you don't have to worry about pulling a wet shirt over your head if you go into the water) in a light color (to reflect the sun, rather than absorb it).
If the skirt is not long enough to pass for a dress, then a beach dress, or a shirt/ pull on shirt combo is a good way to go to cover the suit appropriately to go into shops.
And, of course, a healthy helping of sunscreen lotion is the best accessory to prevent tanning and skin cancer. Remembering to reapply as directed, and after being in the water (even if it says water proof).