I'm not an expert, but as Catherine says, you only charge VAT if you are VAT registered. If you are VAT registered, you effectively are an unpaid tax collector - you charge VAT on your sales, deduct from it the VAT you have paid yourself on your purchases, and send the rest to HMRC.
My understanding is that the VAT rate depends on the product or service. Since you as a business effectively collect VAT from your customers on your sales, you aren't paying it yourself, your customers are, so any sort of relief for small traders would not make much sense to me.
There is, however the crazy
VAT margin scheme applying to works of art, collectables and second hand goods to confuse the issue.