I use a 400w convertible MH/HPS light
The reason I asked is if you used a 600-watt or a 1000-watt I would say you might want to try one of the dual filament bulbs that are both MH and HPS. The 600-watt is 300-watts of MH and 300-watts of HPS and the 1000-watt is 400-watts of MH and 600-watts of HPS. I thought that might be a better option for you for getting a mixed broader light spectrum for your plants.
But using a 400-watt you could go with an AgroMax 400 watt High Pressure Sodium Bulb. It puts out 55,000 lumens and adds an additional 30% more "blue" spectrum over standard HPS bulbs.
I can understand the desire to keep down what wold be normal flowering stretch but being in flower your plants do wand and need more HPS light spectrum so I was thinking of ways to give them what they want and need the most and give you at least some of what you hope for too.
No matter what you do the natural growth spurt in flower, that people like to call stretch, is genetically coded so you will only be able to limit it so much no matter what you do and it's not worth not giving your plants what they want and need the most while in flower trying to fight genetics.
If you want shorter final plant height, veg for a shorter length of time, but give your plants the light spectrum they want and need the most in flower. They will like it better and they will thank you with better production and higher quality.