Confusion about SMPS

At first I apologize for my ignorance and any stupid question.

I want to make an SMPS for me (converted from the mains, 230vAc).
There are endless design schematics on the net.
But their inputs are much lower than 230v.
I'm confused whether I need to step down it (using low frequency Iron core transformer which are heavy and less efficient) before the high frequency SMPS transformer. or
I should connect the SMPS transformer directly to the rectified mains (which would be around 300v) and draw power using Mosfet (driven by PWM).

The second thing I want to know is about ZVS
does the switching done when the mains voltage (or pulsating DC) is 0V (when the frequency of the converter would be equal to the mains (50/60Hz)). If so would it have the efficiency of SMPS (which uses high frequency switching).

SMPS come in many types.

DC to DC: example 24V to 5volt.
AC to DC: 110/220 to 5V
(many more types)

ZVS: zero voltage switching (could be done at the 50/60hz power line frequency) BUT Every one that I have made switches at a much higher frequency. 100khz to 2mhz. This is complicated; through inductors and capacitors, a situation is set up where the MOSFET or transistor is turned off (or on) when there is no voltage across the part. This is complicated and not what you should do for your first power supply.

Building a 'power line' SMPS as you first is very dangerous. Things can go wrong very fast. If you want to learn, I think you should get a 220 to 12 volt transformer, add a fuse, and then build a DC to DC SMPS. Getting off the power line may save your life. Keeping the voltage below 50 volts is much safer.

Building a 240V line-powered SMPS is not something I would attempt, even with 50+ years of electronics experience. It requires lots of specialized components and is dangerous. Besides, ready-made ones are cheap. I would not appreciate my neighbor building one either. I am a Ham, and the last thing I want is some newbie next door building an unauthorized transmitter....