Just get a cheap raincoat from Decathlon. Cheap waterproofing is usually done by having a chemical coating that wears out over time, so you will have to keep buying new one when the time comes. Waterproof gears really can't be that breathable, which is logical given that it has to block water from seeping in. Even the most breathable (and expensive) Gore-Tex is only relatively breathable compared to other waterproof gears, it still isn't gonna feel like wearing a T-shirt, so I am afraid you'll have to bear with it.