I stumbled onto this single gear cassette (https://www.amazon.com/Cyclingdeal-Conversion-Shimano-Adaptor-CyclingDeal/dp/B006WRW45O) on Amazon for Shimano freehubs that should make the conversion easier. I'm also sure that other companies (including Problem Solvers) make similar items.
This would let you keep your existing rear wheel, remove the dérailleur, and shorten the chain to make the conversion.
It would also let you keep the multi-gear cassette and dérailleur if you ever decide to switch back, or to make the bike more valuable when you sell it to help pay for your next bike.
Just remember to keep both front and back brakes to help you avoid becoming a Human Hood Ornament when your encounter inattentive drivers who are paying more attention to their phones than their driving.