Vi-Spring 'Tavistock' pocket sprung mattress on a platform base.

We are finding the vi - Spring pocket sprung mattress is too firm on the unsprung base and we have discovered that it really should not be on a firm platform base, as this is what is making it feel too firm. Are there any bases available which we could use with our vi-Spring pocket sprung bedstead mattress, as it is in excellent condition and we would prefer to change the base rather than the mattress. Many thanks.