It's obviously different and this has made me realize that playing a lot of notes on anything fretless needs to be done with a lot of thought, and the high notes are not only hard to intonate, it's hard to sound good without sounding like a quasi fretted instrument.
Your onto something important here.
Intonation will come with time and practice...IMHO much quicker if you play only one fretless instrument.
I struggled with intonation when switching between the NSD and string bass. After a few days of practicing exclusively on one, my intonation would become solid again. As a result I tended to avoid playing the NSD in concert band settings where I couldn't clearly hear the pitch and adjust. In big band settings where the bass is much louder and easier to hear, I would routinely switch between electric, string, and NSD bass.
To work on intonation, I used to practice etudes with a tuner that produced a pitch. With most etudes I preferred setting the tuner to produce the 5th of the key, but sometimes the root worked better. Setting a tuner to produce a pitch and playing intervals and scales is also good practice. You can also hum tones while you play if you don't like using the tuner.
I believe this is an area where playing scales on one or two strings will help you, as you must learn to change the spacing between your fingers as you move up and down the neck without thinking about it. For now your hand should always be essentially in the shape of a partially open claw with all fingers curved and held on, or just above the strings. As you play in higher positions, the spacing between the fingers closes; as you play in lower positions, the spacing opens up. Practice slow enough that you can play perfectly in tune. At first you will need to hear the note first and make adjustments, but with practice your hand will become calibrated and your fingers will change spacing automatically. Increase speed as your skill improves.
When you become really advanced, you may consider studying the rules of tempering and practice playing intervals slightly sharp or flat.
Later you will want to work on vibrato; but for now play without it, so your intonation can settle in. Vibrato conceals intonation problems and also uses a different hand structure that is not as stable as the claw.
Don't forget to experiment with the position of your plucking hand as well. The pitch should become less stable as you pluck farther from the bridge.