Hi,
I am a Mechanical Engineer working in the field of Industrial Design for past 8 years. Please view my work samples in the freelancer.com portfolio here: https://www.freelancer.com/u/gurvindersharma.html
From my understanding, I think you need a tool/accessory to adjust the button loop location so that trouser or skirt can be buttoned up for different waist sizes. I can design such device. Please correct me if I am wrong.
I can also provide photorealistic renders for visualization purpose with appropriate textures, colors, lighting, backgrounds and camera perspectives.
You can also contact me via Email, Skype or Phone. I look forward to hearing from you.
Regards...
Gurvinder Sharma