Memberhsip Site with Zoho

Hi,

We sell our product via a membership site. In the member area, we basically will have a simple customer portal where the customer/ member can edit their information from Zoho subscriptions (ie. Credit Card details, names, ect.). We are still struggeling on how to set this up as we dont want the member to leave the domina and have a seamless integration. Options:

a) Have a complete membership portal on a seperate domain, which gets pulled into the website via an iframe.
b) The html pages get setup on the main website member area. The pages then pull/ put the informations via API.

Can anybody advise what is best practice?

Thanks in advance!
Ricki