AST ends, SPT starts - what paperwork is needed?

Hi. I have a AST ending soon. The easiest option is to let it run into a monthly SPT. However, I am not clear on what paperwork needs to be issued in this case. The tenant has a guarantor, and deposit is protected. Some articles Ive read suggested that an SPT is a 'new' contract in its own right, thus requires the reissue, or signing, of certain docs. There is so much these days required to stay 100% on the law, I need some help! Can I just ask the tenant if they are happy to stay, and leave it at that, if they say yes, or will I need to reissue some paperwork? (and include the guarantor). Many thanks for your help.