The only insurance you need, unless you are employing someone is Public Liability.
I am not sure if it is actually a legal requirement (unlike Emplopyers Liability) but many commercial customers will require proof that you have it, and it is only common sense to have it anyway.
best place? Not sure about the best place, I myself use Stroud & Swinton (not the building society which is The Stroud & Swindon) They are nationwide brokers and they have always found me a good quote.
Ian