There's nothing wrong with Coopers yeast. It may not be for every occasion but that doesn't make it bad.
Don't use the whole yeast cake. Pour it into a sanitized jar and keep it in the fridge until you're ready. If it's real thick it needs to be thinned with pre-boiled water to the point it can be swirled. After you swirl it, let it settle for 10-15 minutes and it should start to layer. Use a sanitized tool (baster) to pull about 150-200ml of slurry that makes up the middle layer.
If you use the whole yeast cake and it blows the top off your fermenter, it'll serve you right. That's too much yeast. Even with the 150ml of slurry you need to start fermentation off in the lower temp range.