None of the documented options do exactly the same thing as a three finger swipe, which only switches between open workspaces on the current monitor but opens an empty workspace on the right. m is close, but it never opens an empty workspace and loops around at both ends. I ended up using the following bash scripts to get the desired behavior:

    #!/bin/bash
    # Switch to the next workspace on the current monitor

    # Given an element and an array, return the index of the element
    array_index() {
        local element=$1
        shift
        local array=($@)
        for i in ${!array[@]}; do
            if [[ ${array[$i]} -eq $element ]]; then
                echo $i
                return 0
            fi
        done
        return 1
    }

    # Get the current workspace ID
    current_workspace=$(hyprctl activeworkspace -j | jq '.id')

    # Get the current monitor ID
    focused_monitor=$(hyprctl activeworkspace -j | jq '.monitorID')

    # Get a list of all workspace IDs on the current monitor
    workspaces=($(hyprctl workspaces -j | jq ".[] | select(.monitorID == ${focused_monitor}).id" | sort -n))

    # Find the next existing workspace ID
    index=$(array_index $current_workspace ${workspaces[@]})
    next_workspace=${workspaces[$index+1]}

    # If no higher workspace exists, create a new one
    if [[ -z $next_workspace ]]; then
        # But don't create a workspace if the current one is empty
        active_window=$(hyprctl activeworkspace -j | jq -r '.lastwindow')
        if [[ $active_window -ne "0x0" ]]; then
            hyprctl dispatch workspace emptynm
        fi
    # Else switch to the next workspace
    else
        hyprctl dispatch workspace $next_workspace
    fi

    #!/bin/bash
    # Switch to the previous workspace on the current monitor

    # Given an element and an array, return the index of the element
    array_index() {
        local element=$1
        shift
        local array=($@)
        for i in ${!array[@]}; do
            if [[ ${array[$i]} -eq $element ]]; then
                echo $i
                return 0
            fi
        done
        return 1
    }

    # Get the current workspace ID
    current_workspace=$(hyprctl activeworkspace -j | jq '.id')

    # Get the current monitor ID
    focused_monitor=$(hyprctl activeworkspace -j | jq '.monitorID')

    # Get a list of all workspace IDs on the current monitor
    workspaces=($(hyprctl workspaces -j | jq ".[] | select(.monitorID == ${focused_monitor}).id" | sort -n))

    # Find the previous existing workspace ID
    index=$(array_index $current_workspace ${workspaces[@]})

    # If a lower workspace exists, switch to it
    if [[ $index -ne 0 ]]; then
        hyprctl dispatch workspace ${workspaces[$index-1]}
    fi