Right outside the gates to Suran, you will find a pack donkey seller with three donkeys for sale. Buy as many of them as you like. The pack donkeys are using a script based on Grumpy's latest warping scripts, so they are excellent at following. Thanks to a special ring, they can also recall to you (exteriors only). They are peaceful animals, so they won't join you in battle unless they get directly attacked. 

Previously, Cait's pack donkeys have had a tiny problem - they have been shaking their heads whenever in companion mode.

But, that problem no more exists. Cait decided that she wanted to upgrade her donkey models in order to make them better companions. Here, you can see the result for yourself. 

Visit Cait's website and look at her beautiful animal models!

Others:

If you levitate, the donkeys will be there when you get back.

They swim... Sort of. And they have the water breathing ability.

You can heal the donkeys with healing potions if you have them in the inventory. But as they aren't fighters, this probably won't be necessary

They level (sort of). Their attributes will be set to match your level on initial meeting. After that a check will be made every time you sleep to adjust stats. This happens automatically. No message boxes.

Health % can be determined via dialog.

Download Pack Donkeys
from Emma's Elder Scrolls Site