What ever you do £7,500 of that income is tax free. Thats money in your pocket. But you must look at your additional expenses with having two lodgers. I have done this and the biggest expense has been Cleaning materials! I kept my cleaning material receipts separate and totted them all up at the end of the year. Everything from Fairy liquid to window polish. I mean everything! I provide toilet paper (bulk buy from Groupon) and cleaning stuff for them to clean their rooms with. I dont provide anything else - not linen or toothpaste!
My rented rooms are large so I bought 2 IKEA two seater sofas second hand off Ebay @ an amazing price of £10 each and put slip covers on them, added a nice coffee table. So I don't share my lounge. I change tea towels and bath hand-towels daily because of hygiene and that adds to the washing. (cleaning materials again)
Eventually I got a cleaner every fortnight as I was exhausted trying to keep the place pristine (more costs!) My children had chores when they lived at home whereas Lodgers do nothing!
I suggest you read everything on www.Spareroom.co.uk and www.theaccidentallandlady.com for tips. I only take students a) because they do not pay council tax so you do not loose your single person discount but you have to send the student registration to the council and b), because they go home to their parents in the holidays and c) because I dont want anyone staying more than a year. I take a boy and a girl for balance. I have only had to give one person notice. I use a Licence Agreement never ever use an AST its incorrect for Live In Landlords. They have to sign the Inventory and the House Rules which I now call House Notes as it softens it a bit! Always Always take a Depist/Security/Bond and never ever spend it no matter how tempting. Its not your money but the interest (joke) is yours!
No overnight guests are permitted ever. I actually say in my ad, if you want overnights guests please don't apply for my rooms. I will allow a parent or sibling to overnight if asked in advance, but having had one early lodger shagging his girlfriend all day and night over my head very loudly for weeks, was not something I was prepared to go through ever again! I have an annual two week break to refresh (paint, deep clean) re-think and enjoy my house with dinners for my friends and family. When my students are gone they are gone. Next..!
I have found it to be successful and far better than being on the dole. I can pay all my bills on time and best of all it got me out of serious debt. My children are grown up and its my income. Its a business for me.