The crank you have on it will be convertable i would have thought. Just remove the chainrings you dont need and run a single one.
Ho many gears (on the back) does it have at the moment?
If its 8 or 9, then removed them all and add the spacers plus one of the cogs.
Its tricky to run geared frames without a doofer (tensioner). I managed it on my bike, but only because I was running a half link (included in the sale) to get the right tension. However, after time all chains stretch so then you have to use a tensioner to tension the chain.
However, if you have used a half link then there wont be much slack in the chain anyway, so you can tension the chain ‘upwards’ which makes more of the chain wrap around the rear cog. If you have to much slack in the chain then you have to tension downwards which isnt great because theres less contact between the chain and cog and this can make it skip when pushing down hard on the pedals, and this sint a nice experience.
Some bikes you can get the perfect tension without a half link (not often) but the chain will stretch eventually, which is when you bang the halflink back in to regain tension