We *strongly discourage* you from configuring your domain using A records and IP addresses, it will prevent your domain working in future as we expand the SupaDupa platform.
ALL domain name providers should allow you to use CNAME reccords for your 'www' or 'shop' sub-domain, the CNAME should point to 'mysupadupa.com.' (note trailing period, it may be required in your domain providers system).
If you think you need to enter an A record for your domain root (e.g, example.com without the www prefix), please check again - your domain provider may offer a domain redirect feature that allows you to leave your domain root pointed to one of their servers, which are then able to issue a HTTP 301 redirect to the www.example.com version of your domain.
If you domain provider offers this, we strongly recommend using it.
Most full featured domain registrars to offer this feature free of charge, including Godaddy and 123-reg.