I actually just made one last week for my baby girl's 3 month pictures. It came out SUPER adorable
& I was very proud of myself!!!
Since it was for personal use, I just used a diaper cover that came with one of her dresses ;p Not that you could do that for selling purposes, but if it's for your family member then that shouldn't be a problem. The way I did it was by sewing each flower to the back... You can see the stitch when held up close, but it does NOT come out in the pictures at all! I had originally stitched them on the back like the Etsy one you posted, but then she didn't want to cooperate on her tummy, so I just flipped it around and put it to her front. It looks gorgeous!!!
Now, sewing was very time consuming and like I said you can see the stitch, so if I were to do one again, I would definitely think of gluing instead.
Good luck on yours! post pics when you're done. I will definitely post pics when I get them bk from the photographer