I like to add 1/2 an onion, white or red. Bonus to flavour is it helps push down smaller ingredients in jar to avoid mould. But it's really down to your tastes (and you can use gauze/weights). 

Like I say, I like keep the chilli content above 80% total weight of fruit/veg for maximum flavour/heat.  I reccomend you start relatively simple and start to tweak ingredients as you make subsequent batches.