Not only awesome Word Bearers, but also Thousand Sons from you? Sub'd instantly.
As for adding new stuff - when I was returning to my Chaos army in 2011 I was choosing between Night Lords (then I read DtD blog and the rest is history) and Thousand Sons, so I actually was thinking about the same problem as you. So first, as Kraut has already mentioned, terminators and tzaangors, you can never go wrong with those. Another possible option is Thousand Sons warcoven taken from the old Apocalypse book: a unit of chosen sorcerers (so in terms of rules they could be chosen looking like sorcerers). According to the 3.5 ed 'dex TS could not use Raptors, Havocs and Bikes, but I think any other unit from the dex will fit just well for them.
Oh and don't forget tons of horrors.
Hope my opinion will help you somehow. Good luck with this project!
Edited by DarkVen, 17 August 2016 - 07:20 PM.