What temperature rise are you designing for? Is 35um your finished trace thickness, or are your traces plated up thicker than that? IPC-2221 indicates 0.3mm for a 10C rise in 35um copper at 1A, or 0.15mm for a 30C rise in 35um copper at 1A. This standard is widely accepted and generally agreed to be conservative. If you want a more aggressive estimate you might try referring to IPC-2152, published last year. That would allow you to obtain a more accurate estimate, but requires more information about your design such as indication of the substrate thickness, substrate material, whether you have planes present, whether you are running an array of parallel conductors, etc.