'99 8 door suburban;how to upgrade seats?

[nikny]

I just bought this unique and rare factory built car. The seller told me that 30 were manufactured by GM who sold 28 to Saudi Arabia. I got one of the 2. It was designed with four rows of benches. It has the front bench but the others are not there. I may want to remove and install buckets for the front in the future in which case I am asking you folks
1) what is the latest model front seats that would fit with ease?,

but more importantly I need to buy three bench seats for the passenger area, and want newer model seats that have the built in shoulder harnesses. Ebay has plenty of junk yard seats in good condition.

2) Which model and year would fit or what modifications are necessary to make a newer model seat with shoulder harnesses fit in my '99?

thanks.