For a simple WSFC clustering solution with low hardware requirements with RDMs, you might choose to have one standby host.

Set up your system to have a virtual machine corresponding to each physical machine on the standby host, and create clusters, one each for each physical machine and its corresponding virtual machine. In case of hardware failure in one of the physical machines, the virtual machine on the standby host can take over for that physical host.

The following figure shows a standby host using three virtual machines on a single ESXi host. Each virtual machine is running WSFC.
Note: This solution is not applicable for vVol and clustered VMDKs.
Figure 1. Clustering Physical and Virtual Machines
Table shows clustering of physical and virtual machines