You'll get the same services as in the UK. In fact my Tunisian wifi is faster than I get in rural Scotland. There are various price structures according to your needs, you spoke of unlimited downloads, an option which will cost more. There are other companies but look at orange.tn for some ideas.
We have Global Net but we live in Tunis so I am not sure if they are everywhere. We have been very happy and their customer service is great, a rarity for Tunisia! I think we paid 200td for a year with a speed of 8mbps.