While the majority of buy-to-let mortgage providers base affordability on projected rental income, some will only agree to lend if you bring in a certain amount from other sources - regardless of whether you intend your investment to be self-funding.
If you don’t receive any additional income, seek advice from a broker. They are familiar with the buy-to-let mortgage market, and can point you in the direction of lenders most likely to consider applications based on rental income alone.