Since the http:// sites are 100% static, there is no need for https.
Except that an attacker can impersonate your website. There are a whole host of attacks that are possible. E.g. an attacker can inject javascript into the website to mine cryptocurrencies with the users browser while they visit your website or more overtly could embedd advertisements to gain money from the people visiting your website. Or an attacker could use the trust the user has into your website and trick people with scams, e.g. advocating for some dubious services or something. A bit more malicious they could provide downloads which contain malware or link to malicious websites etc.
HTTPS is not just encryption, it's also authorization. While DNS certificates are just domain verified, certificate transparency (which is a requirement for CAs to be accepted into the browsers certificate stores) ensures that no two certificates should be issued to the same domain. Additionally you can register a DNSSec entry, with the CA you get your certificate from, to ensure that no corrupted other CA impersonates your website.
Even static websites can be dangerous. I mean your website is quite small so the risk is negligible, but image a news website from a big news organization. News articles are 100% static, yet someone who could just put anything up on such a website, any fake stories, any scams, etc. could seriously do a lot of harm.
Static or not, HTTPS should always be used unless in very specific circumstances (e.g. on calls to localhost, or extremely small local networks), especially as Let's Encrypt makes it completely free