Do a search in this forum for "iWeb replacement" and you'll get many discussions about potential apps to replace iWeb.
Julian ~ Consider the free Weebly. Since it's browser-based, you'll be able to update your site from any modern Mac or PC. Weebly's net promoter score — an industry calculation of how likely users are to recommend a service to others — is an unusually high 80%. (Source)
You can get an idea of Weebly's capabilities by looking at their featured sites.