Hello Cath -- welcome to MobileRead. Don't let the Mac be a put-off for getting a Sony. The device itself works just fine with the Mac; you can transfer files from the Mac to the Sony PRS-505/700 just fine. You can use Calibre on the Mac to manage your e-Book collection.
You might want to start your research on various devices by looking at
E-book_Reader_Matrix in our Wiki.