Trees are small or not depending on how they are kept. Ficus is the classic indoor bonsai tree. Kept pruned and root pruned in a tiny pot it will stay 6 inches tall or 12 inches or however many you allow it to be. But you could take your 12 inch tall ficus bonsai and plant it in the ground and in favorable conditions it will start growing again and end up 100 feet tall! Other trees that are often used as indoor bonsai are serissa (thousand stars tree), dwarf plum, brush cherry, carmona (fukien tea), chinese privet.
For tips, please start by reading this thread, general bonsai growing tips: viewtopic.php?f=36&t=1479
There is also a lot of good bonsai information in the non-forum part of this website: https://www.helpfulgardener.com/bonsai/
Please buy your tree from a reputable bonsai dealer, even on-line, not a big box store, even if it costs more. Much of what is sold as bonsai are small cuttings from junipers and other trees, stuck in a pot and rooted. They have teeny-tiny root systems and have not been well cared for. And don't let anyone tell you that a juniper tree is an indoor bonsai. They die indoors.
I would look for a pre-bonsai tree. These are trees in nursery pots (not tiny bonsai pots) that have been given just a first general shaping. (See https://www.bonsaiboy.com/catalog/pre-bonsai-trees.html
for examples). They are available cheap and they still have room for you to apply some of your own ideas and techniques to them as opposed to just maintaining a basically finished tree that someone else did. You will learn more and will have more sense of accomplishment that way. Alternatively nurseries at the end of the season often sell off their remaining trees and shrubs cheap. Get a regular tree or shrub and you can do all the work of turning it in to a bonsai. More difficult for beginners, but lots more learning. And if you kill or ruin a few (which is likely in the process of starting to learn the art of bonsai), no big loss.