How to preserve font weight when converting from otf to woff/woff2

So I have some fonts in otf format and when they are converted to woff/woff2 their weight changes, the problem is their otf versions are too heavy 130 kb more or less, so I need to convert them to improve performance.
Tried so far with Font Squirrel | Create Your Own @font-face Kits
which fixed an offset in vertical alignment (thanks to their help) but even using export mode and hinting doesn’t fix it. I have tried with the official woff/woff2 versions but they have as well different weight when compared to he original of font files.