Please help with setting advance animations (start running & jumping, stop running & jumping, turning left & right, idle for right and left positions)

can I ask a (maybe fool) question? How do you guys manage to set specific custom transitions in between animations so that you get smooth transitions? (with the Animator or whatever, I'm willing to download any other asset/app that helps). Let me explain:

I'm coding a 2D side scroller in a 3D space with Bolt, and so far I have one animation for idle (detected when not moving) and 2 running animations: rightwards (triggered by positive speed input) and leftwards (negative speed input). How can I implement turning left and turning right animations? I can't come up with any parameters that go well with idling and running.

Moreover, I would like to add a second idle animation when facing left because the character is not symmetrical (that's why I had running leftwards), I also want to add "start running", "stop running", "start jumping", "stop jumping" animations but again, I don't know how to implement the parameters and code them with Bolt. Also, it'd be great to get the stop jumping animation to trigger when you release the jump button.

I would appreciate any help or suggestion! Thanks in advance!