Where can I store my documents and other valuable materials as I need more working space and is storage solution providers a good option?

Iron Mountain is probably the top firm, in this area.

You might also consider scanning the documents and just maintaining the files electronically. But such a plan requires a very strong disaster recovery plan.

I agree, is it really needed to have the paper file, can they not be saved electronicly ?
Pe
But there are many off site document storage companies, and some companies use private climate controlled private storage facilities. Depends on what type of files and security required on them.