Thank you very much everyone for the insightful and prompt responses - much appreciated!
Hmmm, well, back to the drawing board then! I had originally seen this as an opportunity to sample TK J but was put off by the 14h05 outbound (the inbound is a more-palettable 7h20 with 2h15 to make the connection in IST).
However, it sounds like a protected ticket is a must here - especially with the additional security checks - so will just take the TK option and build in an overnight in Istanbul.
Thanks again everyone!