For simple snorkelling, I prefer traditional rubber full-foot fins and over the years I've found several models to accommodate my long (US size 12) and broad feet. Escualo Sports Clasica fins are my current favourites, but they're hard to get hold of outside Mexico:
There is a range of broad-fitting fins within this category, however, from Speedo Trialons, which are light and float:
to Apollo Uni full-foot splits:
Don't feel obliged to follow my choice of fins. Much will depend on your own expectations when it comes to materials, pricing, blade flexibility and the snorkelling activities and venues. Snorkelling fins are worn for power, endurance and manoeuvrability, although individual models rarely satisfy all three criteria. There's no substitute, as you have doubtless already discovered, to trying on, and trying out, fins for yourself, with socks or booties if you are planning to wear them underneath. Although finding the perfect snorkelling fin can be something of a voyage of discovery, I've chanced upon several perfect fits over the decades.