Being in the UK, you probably have at least a couple of choices that are subsidized by your local electrical utility company...I'd look into what they have available first. IF you have enough spare power coming into your home, right now, as far as I can tell, the i3 is maxed out at 7.4Kw, which is about 32A with your typical acv power input. Some have implied that the 94ah version of the i3 has a larger internal charging circuit, but some other sources say it takes longer to charge than the smaller unit, so that implies it's the same. It doesn't hurt to have a larger EVSE, as the car will only use what it wants, sort of like plugging in a 50W light bulb into a circuit that could also support an electrical space heater drawing 1,500W...there's a signal from the EVSE that tells the vehicle how much power it can safely supply, then the vehicle decides how much, up to that limit, it wants to use. IOW, an EVSE that is larger than your vehicle can use won't hurt anything, but it won't cause the vehicle to charge any faster.
The other things to consider are whether you want a tethered cable, and how long it would need to be to reach your vehicle. Many, but not all, EVSEs are rated for external installation, but the installed cost is a bit more because of the way they need to be wired verses using the same thing internally in a structure.
Some of the EVSEs have extra features like WiFi or Ethernet connectivity, that let you monitor and control the operation. SOme have an internal meter to show you the amount of power used. A basic one just has a few idiot lights to tell you if it is powered, charging, or there's a fault.
