I am joining a high level campaign (ECL 19) playing a succubus 10/ Fiend of possession 6/ Uncanny trickster 3 (advancing succubus monster levels). Not the most optimized character, especially since the house rule allows you to jump out of monster class progressions before completed, but the DM is stoked about the idea of a full succubus FoP and I am looking to play support. The plan is to keep the other players and PC's in the dark as long as possible about my existence. To this end, I need an NPC to carry me around. Psionics are out which is why I did not go the thrallherd. I took the leadership feat and improved cohort. I tried to mitigate my LA as much as possible with uncanny trickster advancing through the last 2 levels of Succubus which are pure LA (Weapons of Legacy is not an allowed book, which would have allowed full LA mitigation with Legacy champion and the house rule, eventually).
Unfortunately even with my tricks, my character level is 15 and I can only recruit a level 14 cohort. Then I saw the Undead Leadership feat and got really excited for a moment. Cohort based on ECL instead of character level would be great, but am I reading that correctly? And is it only for undead cohorts, not living cohorts obtained through undead leadership? I did not see any threads covering this specifically. Any suggestions on ways to further boost my cohort's level? Thematically an actual undead cohort is not going to work in the campaign very well.