So I managed to obtain the TK Record locator from LH and that did the trick using TK Android app. I was able to select seats in Biz on both flights. Appears the European flight is currently to be operated by a 78B version of the 737-800 with 16 proper recliner Biz seats, but given TKs aircraft roulette I'm not holding my breath (fingers crossed though). The long haul is currently an A333 and hoping it stays that way and not that an old A332 with the angled flat Biz makes a last minute appearance. Again, fingers crossed. Connection in IST would be ~3 hrs so should be fine if nothing major happens.