Dear Manu,

Here are some articles that can be helpful. For the last two links, you can directly contact the main author to send you the article.

http://www.personality-project.org/revelle/publications/rafaeli.gotlib.revelle.pdf

http://selfdeterminationtheory.org/SDT/documents/2005_RyanLaGuardiaRawsthorne_NAJP.pdf

http://www.psych.ufl.edu/~shepperd/articles/JP2004%20Complexity.pdf

http://link.springer.com/article/10.1007/s12144-014-9285-7

https://www.researchgate.net/publication/23673275_Measuring_self-complexity_A_critical_analysis_of_Linville's_H_statistic

https://www.researchgate.net/publication/40694445_Validating_a_New_Measure_of_Self-Complexity

With my best regards

Prof. Bachir ACHOUR

Article Measuring self-complexity: A critical analysis of Linville's...

Article Validating a New Measure of Self-Complexity

you might also want to look at the theory of general self-efficacy, coping strategy inventory, LASSI and maybe personal development theory _key cognitive strategies, key content, contextual awareness and skills, just to name a few 

Regards

Tumz

I have received any practical tool yet, if you have one on Self- Complexity kindly share.