I have the same issue and your solution seems perfect but i can't get it to work. can you tell me what CSS i use and where to put it? In an different thread someone recommends this below and putting it in the "advance page settings", I assume on the main page that people will be directed to, then this should automatically put them on the mobile version?
<script type="text/javascript">
if (screen.width <= 767) {
document.location = "https://google.com";
}
</script>