With a Gross income of less than £500k you don't need to be audited but you do need to have your accounts independently examined.
Having your accounts drawn up by an accountant would satisfy this requirement and a well kept spreadsheet would be enough, along with the hard copies of evidence.
I'd set up 4 pages, with the headings supplier ledger, bank payments, bank receipts and customer ledger (depending on what you'll be doing)
Supplier ledger, you list the company name on the invoice, invoice number, date, amount and what it was for.
Bank payment, you list the date paid, cheque number or if it was made by internet banking, amount and what it was for (if it was a purchase payment for an invoice then list the invoice number)
Bank receipt - date, amount, what it was for, if it was in response to an invoice you sent out then match it to that.
Customer ledger - invoices you send out to customers (including grant making organisations)
Don't forget to check your bank statement against the listed transactions each month and if you get funding you can always work the cost of business support into any application.
In terms of packages, I use Sage for our charity and it works very well but we are quite a bit bigger.