If you are moving to a smaller house, you will likely need a storage space for some of your things. It's also possible that some of your things won't go well with your new place so you can opt to store them for a while until you decide what to do with them.
Self-storage units are generally more expensive but it allows you access to your things at any time. This is ideal if you have inventory that you'd want to get hold of every so often. On the other hand, warehouse storage is appropriate if you don't need to have access to your things until the time when you want to get them. Since it's cheaper, this makes it the ideal option if you are going to store your things for a longer time.
Space versus Cost
Even if you are conscious of the cost, you have to make sure that you have enough space for your things. It would be unreasonable to rent a space based only on price. But to make sure you are not wasting your money it would be a good idea to talk to the owner of the storage facility to consult how much space you'll need by telling him what you are going you store. Of course, the removals company can immediately tell you about it when they come to assess or pack your things.
The thing is self-storage is usually rented by unit. If your belongings will take up more than one unit, you would have to rent two units even if you don't fill the whole second unit. This means you would be paying for some space you are not using.
If you decide to warehouse storage space, you will only be paying for the space you are using. This makes it even more the cheaper option.
Take note of all the details on the contract. You should know exactly how much it is going to cost you. You should also know when the payment is due. Find out if there is also a grace period in case you overlook making the payment on the due date. Some owners are stricter so you should make the payments on time in that case.
Does Convenience Matter?
Location may also be an important criterion for you especially if you need to access your things quite often. You'd want to get a convenient location so it would be easy for you to get some of your things when you need them.