Red Chilli Varieties - Heat/Strength

I often make chilli jam which has proved very popular (especially with the men!).  However, even though I always use slightly more of the large red chilllies than specified in my recipe, I find that quite often the end result is milder than I'd like.

The recipe specifies 10 of the long red chillies (the large ones), so I'm wondering if I used 10 of the smaller Thai red chillies whether that would be better, as I understand they're hotter?  Or half and half??  I usually make at least double the recipe, so I'd rather not have to simply increase the number of the large chillies because they're expensive ... if I could get away with replacing them with the smaller, hotter ones, it would be a bonus!

Any observations welcome!! 

Yes, I've got lots of seedlings on the go - planted them a few weeks back.  However, from what I've read I think it'll be a good few months before I can harvest anything red ... which is of course the colour they need to be for the chilli jam or else it looks as though it's got bits of something in it that it shouldn't have!   

I make a lot of Chilli Jam, and I always go by weight.
Just the same as if it were regular jam, one Kilo of Chilli to one Kilo of jam sugar, plus the juice of a couple of lemons.
I use Scotch Bonnet by choice, or whatever I have available.
I am sure a variety would make a good jam, but I never seem to have the time to experiment too much.
And I always include most of the seeds ( I save a few for next years plants ) for the visual effect mostly, (the heat is actually concentrated in the placenta not the seeds).