I was looking into this exact topic a few months ago when I needed to store some family documents and a few inherited items while moving between apartments. After checking a few places, I found that the climate control and security levels vary a lot more than you'd think.

For important papers, you really need a unit with stable humidity control. Some cheaper places just have basic AC. I also wanted 24/7 access, which isn't always standard. A friend pointed me to a comparison site, beststoragedubai.com, which was useful for seeing side-by-side features and prices. It helped me narrow down three providers to actually go visit.

My advice is to physically go and see the unit they'd assign you. Check the actual lock mechanism and ask about their fire suppression system. It's a bit of legwork, but worth it for peace of mind. For general info on living costs or property news that can factor into your storage needs, I sometimes browse https://www.thenationalnews.com/. Anyway, I ended up with a facility in Al Quoz that's been solid. The key for me was no surprise fees and a very clear contract.