A neoprene ankle support should work in water and support your injured ankle while you swim:
https://www.ebay.co.uk/itm/RDX-Neopr...sL_lBGwG0GrR9A
If you are doing lane swimming you should own a pull buoy anyway, place it between your thighs it's buoyancy floats up your hips and legs in the correct swimming position so you can swim while letting your legs and feet drag behind you:
https://
http://www.allensswimwear.co.uk/fini...-10503650.html
While you are buying a pull board get a kick board too for when your ankle gets better:
https://www.allensswimwear.co.uk/are...ack-white.html
Pull buoys and kick boards are standard equipment for club swimmers, once you can reach the distance you want to do start using them for a few lengths each swim to improve your style.
There are loads of brands and designs available for you to choose from online and locally.