Lots of good advice here. I'll just add a couple of hints.

You could start by putting on a strap and then playing on a high stool, sitting down - which is a halfway house. Here's me doing just that:

Spread A Little Happiness

I'm actually seated on a piano stool with a cushion - which lifts me up so that the guitar can be seen comfortably by the video. Note the guitar height and angle. It's far more vertical than when I play with it resting on my knee. I also prefer a high position - can't play with a low-slung guitar because it makes fretting some notes awkward.

You'll notice, by the way, that my guitar - like others I use - has no dots on the fretboard. If I need a reference position, there are little dots on the side binding - that you can't see! It took me a while to get used to fretboards with no dots, but classical players do it all the time.

So, if moving from sitting to standing poses a problem, try the halfway house of using a strap while sitting on a higher chair. Then, when you're used to that, stand up fully and see how you get on.