Almost any 2-inch or 3-inch racing harness with shoulder belts will work with the G-Belt.

A 5-point harness, with or without the lap belts is suggested. See illustration.

We also suggest obtaining a harness that has springs on the shoulder belt adjustments. These help to prevent the shoulder straps from loosening as you drive. See illustration below:

2" belts will feel more intense than 3" belts. This is because the 3" belts spread the pressure applied by the G-Belt motors over a greater surface area. If you don't have a size preference, we suggest 2" belts, because you can always reduce the G-Belt intensity in software settings if you find it too strong.

Here are some 2"' belts/harnesses/restraints available at Summit Racing:

https://www.summitracing.com/parts/sim-29400bkr1x

https://www.summitracing.com/parts/rjs-1017401

https://www.summitracing.com/parts/imr-57346661

Here are some budget belts/harnesses/restraints available at Amazon:

https://www.amazon.com/BESTZHEYU-Compatible-Shoulder-Universal-Polyester/dp/B08HTZFLYH/

https://www.amazon.com/Aces-Racing-Harness-Padding-Certified/dp/B07TJ8R7FG/?th=1

The choice of racing harness/belts to use with the G-Belt will depend on a few factors, such as the type of racing you will be participating in and the regulations of the governing body that oversees the event.

In general, it is recommended to use a 4-point or 5-point racing harness/belts with the G-Belt to ensure maximum safety and effectiveness. These types of harnesses/belts provide superior support and stability compared to a standard seat belt.

It's important to note that the G-Belt is not a replacement for a racing harness/belts. It is designed to work in conjunction with a racing harness/belts to provide additional support and stability during high-performance sports platform https://mexstrengthltd.com/

I'd highly recommend this belt because the anchors can be easily removed making it very easy to run the shoulder harness through the G-Belt without damaging the belt. 

 https://www.summitracing.com/parts/cws-11152

I've recommended it to a number of other G-Belt users and they have all been very happy with it.