Confusing isn't it!
Lets start with the Zafira. As you dont say how old the Zafira is. I will assume it is the Mk1. Sadly when Vauxhall made the Mk1 Zafira, they didn't give as much thought to towing, and as a result it is only rated to tow a maximum weight of 1050Kg. You must not exceed this figure.
The caravan you have purchased you say has a weight of 1150Kg, but you don't say if it is the maximum or the bare caravan weight.
If it is the bare weight then it is not legal to tow it with the Zafira, however if it is the maximum weight, then you may have a chance by loading it very lightly,and ensuring it never exceded the Zafiras limit of 1050.
I would observe that it is unlikely that you would easiliy manage to keep the weight down, especially when you consider things like the weight of 12 battery, gas bottles etc, cutlery and other esential items.
Realistically you do need to consider a more able tow car, having said that the Mk2 Zafira has a much better towing margin, and if you like the Zafira the Mk2 could be what you are looking for. Also consider the VW Touran, which is a good rival to Zafira.