Hi Gillian, 
 
Thanks for your question. 
 
We would need to know your body weights first and foremost to discuss suitable spring tension with ourselves as the guidelines will differ (even if only slightly) between retailers;
 

 
We have no direct comparison with Harrison as most retailers won't disclose how they construct fully. However, the description of fillings including wool, cotton and mohair would put it in line with our Artisan Naturals. 
 

 
The Naturals is a true medium feeling model in that top layer, similar to the firmness rating 6 for the Harrison, giving a slight sink into that top layer but not too much. As Harrison don't disclose which layer is which it's difficult to definitively say it will feel similar but it should be there or thereabout. 
 
Please note that we don't use HD springs ourselves; These tend to be smaller springs used to bump up spring count. We use Calico Encased Pocket Springs, just as Vi-Spring do. 
 
The Harrison model markets as having a summer and winter side; The Artisan Naturals is constructed using 85% natural fillings and those fillings give a cool sleep surface. We don't retail anything with a summer and winter side. 
 
I hope this has answered your questions fully but if you do have any further queries please don't hesitate to contact our office on 0161 437 4419.
 
Kind Regards, Lee.