I doubt you'd get €300,000 purely on ability to service this level of mortgage. Assuming 40,000 is gross, your take home pay is approx €2700, servicing a mortgage of €300000 would exceed 50% of your take home salary even for a 35 year mortgage after TRS for single person. You could use the rent a room scheme, but I don't think this is going to make that much of a difference, depends on local rents.