If you use Pectin or gelatine to set a 'jam' then it isn't a jam but a conserve. To make a 'jam' you have to add sugar, which does two things - it sets the mixture a bit firmer and preserves the fruit. I didn't
Google to see if this pedantry is correct but it's what's always used in our family.
For the time you spend searching for a commercial brand of jam you could easily make your own it's very simple -
1. Buy as much fruit as you need, pick your own is fun in summer too especially with children.
2. Clean it, dry excess water off, cut into 1-3cm bits or leave whole if you prefer, empty into a big pan with a heavy base
3. Add as much sugar, or as little, as you want. More sugar means sweeter, firmer jam that will stay good longer and may not even need keeping in the fridge.
4. Heat gently until sugar melted and the fruit is going mushy
5. Increase temperature and boil for a while essentially until the fruit takes on the consistency you want, cool, put in clean jars.
If you want really set firm jam then it's necessary to have about 50-50 fruit-sugar mix and boil a bit hotter, but any mixture will become a jam. I do this from time to time with strawberries and it's great. Never bother measuring or weighing anything, you simply can't go wrong and you get exactly what you're after.
Edit: Of course this isn't 'sugar free' but it's free from all artificial crap and despite a few calories is about as healthy as it gets.