Visa Extension

I am married to a Thai national and retired to live in Thailand 3 years ago. The fourth renewal of my non immigrant retirement visa will be due shortly. In the past it was only necessary to show my bank book to prove how much money went into my account each month but I was advised last year that I would require a letter from the pension company this year stating the amount of my pension. I have two pensions one from the government and the other from the Merchant Navy, can anyone advise do I need a letter from both or is it possible to use past correspondance from both and have it endorsed by the British Consul in Chiang Mai.