Be wary with commercial certificates. Standards changed in Q3 last year and most (all?) big certificate providers will now only supply you with a certificate lasting 12 or 13 months. If you buy a 3 year package, you may well still have to renew the certificate annually. I think best practices now say the certificate should only last 12 months, but 13m gives you a bit of time to renew it and get it into place before the next one expires. The big certificate providers now work to this.