Heavy and big? The oscillator/HV coils are quite small -- smaller than the coils in a CFL base. It is typically wound on a toroid with 200 to 400 turns for the HV secondary. The primary and feedback windings are less than 30 turns each. The finished coil is about 3/4" O.D. X 3/8" high. Some people make them even smaller. CFL transformers can be used as can commercial transformers.
Here is a reverse engineered schematic of a popular, non-MCU ignitio from China:
View attachment 69448
This compares the Chinese design to an American design that is currently out of production:
View attachment 69449
You probably wont be using a Hall sensor for your trigger; a simple momentary switch will work. The HV (spark) coil can be whatever you want it to be.
Just what are your size limitations? What is the maximum box size it needs to fit into?
John