I had to put all my house stuff in storage late last year before moving. I promise you that you will need 100 sqft plus! We got quotes for 80 sqft from the likes of spacemaker etc of around £40 pw, then plus vat, plus insurance, and it worked out around £60 pw!
We ended up getting a shipping container that was £24 pw incl VAT, and went for private insurance which worked out at £12 per month! The container was circa 120 sqft iirc too, and although we moved it all in ourselves so it probably wasn't the best to utilise the space available, we just about got it all in. (3 bed house.) It was in a locked compound with cctv, but the only downside was that it was not 24 hr access. (Lets face it, its unlikely you'd need access to it at at stupid o'clock anyway!)
We took a few things to the mother in laws too though so it would have been a really tight squeeze otherwise.
The container was a decent dry vented one, and everything came back out nice and clean and not damp at all. This would be what I'd recommend to anyone.
