Which is the simplest accounting method I can adopt?

The accounting regime which requires the least amount of paperwork and the least number of French tax forms to be completed is the Regime Micro-Entreprise.

This is where 50% of income is taxed at a flat rate of 37.20%, ( 20% income tax rate and 17.20% social charges tax rate), regardless of actual expenditure. It is only the income which is declared.