Thank you gentlemen for your advices and very kind feedback.
I have spent hours experimenting but all results thus far have been unsatisfactory, to say the least.
It looks like I will need to collect more data through S2 and O3 filters. 12nm filters are quite insufficient with increasing contrast from my location though, so I find it quite challenging to create vivid colour images at the moment.
Having said that, my 3nm Halpha works great, so I need to either move away from the city or get 3nm S2 and O3 filters, or preferably both - move to a darker place and get narrower filters
Again, thank you all for your support and encouragement.
Muchos Nachos.