Limiting motion transference and heat retention

The movements caused by way of my girlfriend turning, and generally fidgeting, whilst sleeping often causes me to wake up early and unable to get back to sleep. This has led me to investigating solutions.
Thankfully, the duvet, whilst probably of good quality, is rather old and therefore needs replacing - it's just over 20 years old!
I understand that memory foam is best for motion isolation, but I'm concerned as to the heat retention issue associated with such mattress types.
I've therefore decided on buying a king size zip & link mattress, probably using pocket sprung mattresses rather than memory foam.
Is there likely to be much difference between the motion transference in a zip & link pocket sprung set up and in a zip & link memory foam set up?
Lastly, I understand that mattress toppers on the market can be made of various materials, but that yours are made of memory foam or similar. Could such a mattress topper on top of zip & link pocket sprung mattresses still lead to heat retention issues? And why do you not make other types of toppers made of these other materials?
Thanks in advance, David