downlighters are an inefficient means of lighting, hence you need so many of them (50!)
holes in ceilings allow heat, smoke and flame to pass through what would normally be a fire barrier
LEDs are taking over the world, and you don't have to get transformers.
I'd say, bite the bullet and get on with a changeover to mains-voltage LED lamps, preferably using a fitting that takes a standard bulb, such as Small Edison Screw (SES) that you can buy in any high street. The multiplicity of funny connections, voltages and lamps often used in "modern" trendy lights in unnecessary.
If you want to use dimmers, you need to buy dimmers and lamps that are compatible with each other. They are less efficient in electricity, but the LEDs will use far less, and will run cooler. They will also last much longer, so you will spend less time and effort changing them.
I suspect that dimmer technology will continue moving on so current controls may become obsolete.
If you are determined to have holes in your ceilings you can use fire-rated lamps at extra cost, or use intumescent smoke hoods (these are easier to fit from above, such as from a loft). As LEDs run so much cooler, it might be that they will not start many fires.