Looking to rent an apartment June-September

Nice, tidy, responsible 32 y/o professional arriving to Madrid for 3 months to learn Spanish and looking to rent a 1 bedroom apartment (entire apartment, not room).
The place shouldn't be too luxurious, but should be clean, have an A/C, comfortable 2.00x1.40 bed (2.00x1.60 even better...) and quiet bedroom.

Preferred location is anywhere in the centre - malasana, Tirso de molina and even lavapies.
If anyone is travelling and looking to sublet their apartment, or looking to earn some money on their own apartment during summer. I'm flexible with the price and dates - will appreciate an apartment even for only part of the period (but at least 1 month).

Thanks for your help! :-)