How to fully integrate WHMCS?

I want to integrate WHMCS with our website (WHMCS is so terrible but there aren’t any convenient solutions yet).
I saw that Iframing it is a bad idea, however, I think it’s also a bad idea to directly develop it on the WHMCS portal as WHMCS code is pretty slow at my taste.

What would be the best way to avoid any confusion towards the customer?
For example, I find that once you are logged in it’s really hard to order something else as you need to pass two menus first.
I could also create a custom menu…

How do you guys integrate it?

For making/editing WHMCS, You have to play with its templates available at path/to/whmcs/templates/six assuming six is your template. Also, to editing routes to order and manipulating processes, use Hooks available at path/to/whmcs/includes/hooks. All the documentation for those are given at WHMCS.

Also, there are other solutions like WHMCS. For ex. BillingBox(Cheap), HostBill(One Time Payment) and other free open source as well.

Simple solution to all these problems. Develop one of a kind Client Area, I am also preparing to build one open-source to get rid of this market monopoly.