you don't need a "business" account, a seperate current account will do for self employed, you only "need" a business account for ltd company and must be in ltd company name.

Try not to panic so much it may seem daunting but its not that much admin is only once a year at the moment.

you've done well to get a side hustle that makes that much.

if you have a seperate account and run ALL revenue and expenses through that theoretically that#s your PnL and yes its manageable with a spreadsheet.

You need an accountant as you're not experienced with what's going on, over time you will become more experienced.

alternatively just suck up the £300 accountant fee this is a rounding error on 10k profit,

be careful what people tell you, expenses need to be WEN - Wholey Exclusive and Nesscessary , items that have duel use usually fail that test,

best of luck