I use a $9.50, 5 litre garden sprayer from Bunnings.
I removed the spray wand and replaced it with an adjustable trigger, hand spray. I checked the water temp at our home shower and just heat water to 48/49 degrees and pour it into the garden sprayer. A few pumps and you're right to go.
Wife and I shower using about 8 litres of water.
Works for me.