Host it on Netlify if you're capable of working with a static website system - it's free to host, free to bring a custom domain, and they do the Let's Encrypt integration for you... for free :-)
If you need help, let me know. I'll gladly offer some time to help with a project like this: mc [at] sent.com
No worries, Let's Encrypt makes it really easy if you haven't used them before. Since you have input forms and links to app stores it might be a good idea.