Masha'Allah! Thank you so much for the kind words.
Although one of the most common reasons why there's white smoke is weak valve seals - the oil leaks onto the engine which gets burnt as you start the car, I wanted to replace as many bad parts as I could because I only wanted to get work done once. So, I decided to get the head open.
It was a good decision because as it turned out, the valves themselves had gone bad so got them replaced, the gasket was burnt so got it replaced, head was faced, valve seals were also replaced of course, plugs had gone bad as well so got them replaced as well, there was a lot of mud accumulated over time at the base of the head so got it cleaned as well. All of this costed me around 21k with labour and one full day of work. But the results are Alhamdulillah great!
If your car is really old and you haven't replaced the seals for years then yes, you can go for replacing valves without opening the head IMO. However, if there's smoke coming out and if there are chances that your car might've overheated in the past or something then I would suggest that you get the head open as overheating affects a lot more parts than just the valve seals.
It's an expensive hassle but if done right, it will free you from all your troubles In'sha'Allah!