There's a huge offer of application notes and design guides at powerint.com, in so far I can't agree to your comment. Transformer selection is almost a common problem of flyback converter design and not too specific to TNY278. You should consider however, that the design support documents are primarly addressing professional designers and aren't written as DIY guidelines or power supply tutorials.
TNY278 is a previous generation product, but still a good decision for a small power supply.
The transformer is a dedicated flyback transformer, voltage ratio rather 5:1 than 10:1.