You can claim £2 per week flat rate for 'use of home as office'. That covers everything but I don't know if it includes if you made more phone calls than that amount.
You can also claim 45 pence per mile for every business mile you do - you need to keep records of this.
And you can claim for any equipment necessary for doing your work - eg safety boots. You wouldn't be able to claim for office equipment if it is also a home laptop though. That would be covered in the £2 per week above.
In the past HMRC have done free courses on 'introduction to self employment' that probably covers a lot of this stuff, but I don't know if they still do.
Completing a tax return is fairly simple and once you have done it once, you learn what sort of information they ask for and that can help you set up a spreadsheet to add up your income and expenses in a helpful format.
Do you have an employed job as well? Or if not, did your work earn more than the tax allowance of about £10k per year?
Are you paying the SE NI contributions, although I think these have changed recently - it used to be that you had to pay a couple of quid a week in NI contributions but if you earnt less than about £5k per year from SE only, you could get an exemption certificate to not pay (or you could pay them voluntary as there are pension benefits) but the rest of your NI record would determine whether this is necessary.
I would say if you are earning less than whatever the 40% tax limit is overall and your work is 'labour only' ie you aren't spending money on stock/equipment, it probably isn't worth paying an accountant, but if your affairs are fairly simple, it might not cost a huge amount anyway (£100-200 per year?).