How tall are the terracotta figures of warriors and horses ? Are small figures sold as souvenirs?

Actually, the height of the terracotta figures is almost same as an adult and some are taller. Each of them is generally in 1.8-1.9 m (about 5.9-6.23 ft).
Yes, the small replicas are sold as the souvenirs. If you wanna any, you can refer to this website:
https://www.travelchinaguide.com/shopping/terra_cotta_army/productlist.htm

Choose one you like and click the picture, and you will go to a new page where you can click a certain button to reserve one. Actually, I got one several months ago and I do love it.