How can I avoid limp strawberries?
Apparently, macerating the strawberries beforehand can help. As well as this, the shorter they are boiled the firmer they will stay [1]. 

If you wanted, you could create one jam base and add in extra whole strawberries at the end which will be firmer. Or even still, add them towards the end of cooking so they break down a bit but not as much as the rest.

Source:
[1] http://ewainthegarden.blogspot.co.uk/2010/06/recipes-for-strawberries.html