cant go wrong with booking.com anywhere in europe. aibnb is fine imo but if you dont feel comfortable with it then booking.com is the way to go.
what budget do you have? aussie dollars go a long way in many places in central europe such as budapest, krakow, and i imagine prague but havent been there for a few years. if you leave the major tourist towns and head into the countryside its dirt cheap.
most hotels will be listed online as these cities rely on tourism especially during the peak season which as you point out extends through to september. july and august are the busiest though.
