Financial Requirement - less than 6 months

Hoping someone can confirm my understanding of how the financial requirement for a fiance visa works if you have not been with your current employer for 6 months.

I started a new job a month ago. My current salary and previous salary were both over £18,600 p.a. For the financial requirement, I understand I will need to demonstrate that:

(i) my gross annual salary at the date of application was at least £18,600; and
(ii) over the last 12 months, I received gross salaried income of at least £18,600

Is this correct?

Also, will I need a letter from my old employer confirming salary etc or will it be enough that I have the wage slips and bank statements for the 12 month period? (I will have a letter from my current employer)

Thanks in advance