Can you do Judo without a Gi? Sure thing? Without a GI one thing for certain is that you will have close body contact (especially when hitting is involved). When strikes are included your opponent will either want to stay out of range or in close. When you are fighting a striker, you want to be in either of these 2 ranges. You can force the clinch once the commit to hitting you. Of course you have to risk getting hit.
Without clothing you have the sweat factor. The easiest thing to hold is your opponent's body. I like to get a double under hook or over under body lock. This way I control their center of gravity and I can keep them from getting underneath me.
In this clip from the 2002 Shidokan World Open, I used the body lock and foot sweeps to get my opponent down to the mat. The submission attempts shown will be a neck crank (which he escapes) and later on in the clip an arm lock. Going from the Kimura to a straight arm lock. I will stay with the 2 on 1 grip on his arm.