Any recommendations for Active/Standby ASAs with a single provider ONT

Hi Guys,

First time poster, long time lurker, looking to see if anyone can provide a better idea or some advice for an upcoming network uplift.

For employee recreational WiFi we have a 100Mb BTNET circuit in each of our sites (16 in the UK) hanging off a single ASA 5506 or 5508. I've been asked to increase the resilience of this service by implementing a standby for each ASA to allow maintenance and fault tolerance etc.

However, the line terminates on a single 21CN ONT which we can only have one copper presented connection from (as far as I'm aware anyway). Currently I've budgeted for a number of 8 port 2960CX compact switches. This will also be a single point of failure, but at least we can get site-hands to pull the cable from the switch and direct patch to the active ASA should it fail.

Does anyone have a better suggestion, as weird as it sounds I've thought about those 2 into 1 RJ45 Y splitters that I've seen people use to turn a 1Gig switchport into two 100Meg switchports. But I'm not sure if the ONT will be completely confused by this...

Note, this is recreational WiFi for employees, so a second link is out of the question, we have SecurePlus lines for our MPLS but WiFi is not permitted to use this as it's non-critical traffic, seeing if anyone else has some low cost ingenious suggestions.

Thanks in advance Guys -Ludo