Good Afternoon Kasey, 
 
Thanks for your question. 
 
I wouldn't necessarily rule out pocket sprung mattresses as an option as generally these are considered to be the "better" option for lack of a better word as you get support from the spring inside and then the fillings provide the comfort layer. We'd always advocate trying some comparison models beforehand though to get a good indication of what they feel like. 

Our Artisan range of mattreses compare with the Vi-Spring range that can be found in stores such as Furniture Village, Harrods, House of Fraser or And So To Bed. 

However, we do tend to advise to stick with what you know and like. 
 
Our Fusion range is a range containing 4 models of 100% Natural Latex; Each model feels different in the comfort but from what you note about being side sleepers we generally advise to avoid anything too firm in the top layers as this will simply cause pressure point pains in places such as shoulders, hips and knees. 
 
I would have a look at our Fusions 5 and 3. Both are constructed with a medium density core mattress with the only difference being that the Fusion 3 has a completely detachable latex topper. This will give you an additional comfort layer to sink into before you hit the core mattress. 
 
Please see below for the full breakdown of each model as well the Dunlopillo model it compares with; These can be found in the same stores as mentioned above;
 

 

 
There is no necessity for a topper at this stage - Any new mattress will feel firmer to start with as it has never been compressed. If, after 4-6 weeks, the mattress is still too firm this is the stage we advise to look at adding a topper. It's very much about personal preference as comfort and sleeping habits are very personal. 
 
Please note that if you're keeping the existing base you will need to solidify the base with standard MDF, plywood or pegboard to protect the mattress from indentation and damage. 
 
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. We are open Monday to Friday 8am to 8pm and Saturday and Sunday 10am to 4pm. 
 
Kind Regards, Lee.