You can map your UVs to a smoothed version of your polygon model, where it may be easier to get good UVs (for example, you can smooth out wrinkles which cause overlapping UVs). Then you can use the Transfer operation to copy the mapped UVs back onto the complex original model.

To transfer smoothed UVs between polygon meshes

1. Duplicate your polygon mesh.
2. On the duplicate, select the vertices you want to smooth.
3. Select Mesh > Average Vertices > .
4. Enter a value for the Smoothing Amount then click Apply.

   The higher the value the more smoothing. You can click Apply repeatedly to smooth repeatedly.

5. Project UVs onto the smoothed duplicate model using any of the mapping options in the Create UVs menu.
6. Use Mesh > Transfer Attributes to copy the UVs from the smoothed duplicated back to the original mesh.