I will be going to thailand for 25 days. I know that I dont need a tourist visa for a stay under 30 days but I have previously overstayed by 8 days. Ive payed the overstay fine at the airport ( I wasnt arrested or anything). and everything was ok.

Is it a good idea to get a tourist visa from Hull, uk or is there no point?

Im british and will be travelling from the UK with a return ticket to uk

There is no point. You will have no problems if you stick to your scheduled itinerary. Previous overstays will have no effect on your entry.

Have fun in Thailand.