In 2012/13, after deduction of the personal allowance of £8,105 you would have paid tax of £5,979 (20%) and Class 4 NIC of £2,736 (9%) on an adjusted profit of £38,000.
If you had been trading through one limited company, on profits of £38,000 you would have paid corporation tax of £7,600 (20%) assuming you drew no salary. You could then have drawn the balance of £30,400 as dividend (£33,778 gross) and you would have had no further liability to personal tax as your income would have been less than the 40% threshold at £42,475. You can read about dividends and tax here
You would have saved £1,115 in tax and NIC by trading through a company. If you drew some salary at a level at which you would pay no employee NIC or employer NIC, say £7,500, you would have saved 20% of that figure in corporation tax and still paid no personal income tax as it would have been below the personal allowance. Some like to pay some NIC or at least keep their earnings just above the primary threshold which was £107 per week for 2012/13 to ensure some entitlement to state benefits such as state pension.
The tax and NIC savings are greater at higher levels of profit than you are currently making though the compliance burdens for companies are more onerous, time consuming and expensive if you use an accountant. Whereas as a sole trader you pay tax and NIC on whatever your profit is, if you operate through a company, you can time your salary and/or dividend drawings for the best tax effect, eg you might avoid a higher rate tax charge by delaying a dividend until the start of a new tax year.
Another consideration is that if you ran both businesses through one company, you will have to register for VAT as your turnover is more than £77,000. Running two companies to avoid that would double your compliance burden. Two companies would also be associated for corporation tax purposes which would mean that the £300,000 limit for profits taxable at 20% would be divided by two.
I hope this helps but let me know if you have any further questions.