Dear zoe bunny,
The only safe options for performing buttock enlargement are using your own fat ("Brazilian butt lift") and using implants.
If you a thin person and desire significant buttock enlargement, using your own fat is not a good option because you do not have enough fat to produce the desired augmentation. In this situation, buttock augmentation using implants is your only option.
Having said that, it is important to know that buttock augmentation using implants has potential risks including infection, bleeding, scarring, nerve damage, firmness, implant rupture, implant migration, seroma, etc.
I would discuss your concerns with an experienced plastic surgeon who performs both the Brazilian butt lift and buttock implants.
As an aside, I would warn you about using fillers such as hydrogel, silicone, etc. to perform buttock augmentation. Tempting as they are, they have not been approved for use in the US by the FDA and are associated with significant risks.
Larry Fan, MD