Self-Employed First Time Buyer - Self Assessment??

Hi there!

I'm not "planning" on buying for at least another year, giving me time to grow my deposit further, gain two years financial accounts and by which time my partner should be in a full-time stable job, however, with this financial year soon coming to a close and it being my first, I figured I should seek some advice now on how best to do my self-assessments to ensure we can get a mortgage when we're ready.

I'm a self-employed sub-contractor and primarily work for just a single contractor, I have a few expenses, tools, work miles etc, but nothing to complicated so I figured I'd be able to do my self-assessment myself.

I'm good with paperwork and numbers, and assumed it would be as simple as adding up all my monthly statements from the contractors I've worked for and putting that in income box X, and then adding up my expenses (for which I have all the receipts, around just 30 of them!), which I put into expenses box Y, to equal my gross profit, Z upon which HMRC calculates my tax etc.

However, firstly, is it this simple?

And secondly, should I consider using an accountant to do my self-assessments instead? Will not doing so make it hard for me to get a mortgage when I'm ready?

I've read mixed opinions but no solid advice. I would of thought if HMRC accepts you doing your own self-assessment (hence the name), then surely the banks should too? But do they no trust they're right, as I've heard people say they need to be done by a chartered accountant for the banks to use them, unless this is for those who own Ltd companies with complicated accounts etc?

Not sure whether it makes any difference, but the contractors I work for do also deduct CIS to be passed onto the government, so proof of these should back up my earnings too?

If we have a decent deposit and my partner in a solid job by then too, will it really matter that much anyway?

Any advice on how to move forward the next few years would be really great! I'm getting a lot of mixed messages, but no straight forward advice. I've even been told not to bother speaking to a mortgage advisor at the bank as they won't know much about mortgages for the self-employed!

Thanks in advance,
Joe