Hi Jonathan,
These suggestions are for southern OK / north Texas, depending where in OK you live
Wichita mountains by Lawton is a great place to spend a couple days get a backcountry permit and hike around the basin area. basically prairie over mountains. you’ll see bison, scramble over a lot of granite, and since they only issue 2 permits at a time, have the place to yourselves. Search BPL trip reports for some suggestions.
Sandy sanders by Erick OK has some nice trails and is a quiet, seldom used prairie land with enough miles of trail to hike a couple days, but it’s a network of trail loops, not linear.
LBJ Grasslands by Decatur TX has 50+ miles of trails. It’s a nice place to spend 2 days hiking,I always carry my own water but you can drink directly from the pipes of windmills that fill stock tanks.
Ouachits mountains in SE OK, while not prairie, is a really nice corner of OK for hiking.