If I wanted a space bar that was larger than 1u, I would probably choose a 3u (though I'm not sure how easy it would be get such a cap) right in the middle of the bottom row. You would probably want to put a single switch in the middle and leave the two sides unpopulated (not sure if that does anything weird with the circuitry though). Then customize your layout via QMK (either directly via the source code or via one of the various web-based configurators).
That said, I've been using a 1u for space for over 6 years now, since getting my first ErgoDox. But that works for me and my hands, and it might not work for you and your hands. Luckily, this keyboard has hot-swap switches and QMK, so you can customize the layout and feel very easily.