Your requirements:

• I want to secure commercial transactions / to secure sensitive customer data

We recommend that you use a RapidSSL Certificate

RapidSSL is a 128 / 256 bit single root SSL certificate. RapidSSL is issued using the trusted CA root (owned by RapidSSL.com). RapidSSL is ideal for lite ecommerce- and at only $69, and is the most cost effective SSL solution available.

Click here to view the RapidSSL product page