Since you asked your GF to not contribute by as much money as she does to take care of cleaning instead, it sounds reasonable what sophiesmom suggested to hire someone using the "extra" money she contributes.

If this doesn't work, here is another suggestion: you contribute (monetary-wise) more by your own choice. Doing more in cleaning for her would be her own choice (I assume she does her own cleaning, but not you). If you expect her to do more cleaning because you contribute by more money but she doesn't want or like to, then I would suggest to split everything including costs and cleaning 50-50. This way you both feel you are equal, regardless of your respective income.