Oh gosh yes you need a stool or chair in a greenhouse. Esp for the pricking out and potting on situations. I have a wooden greenhouse and immediately put up 8 shelving brackets and bought 4 decking boards. They sit on the brackets but because I haven't screwed them down, they can be moved onto the darker side for when the tomatoes are growing up the lighter side, but can be moved back for higher up light during the winter for my overwintering seedlings and plants. One of the best things I did...
mine also has staging along one side - it came with the greenhouse, the other I use an old wooden bench for potting on and for plants. They built the greenhouse round it, as it was originally here when we moved. I have several large trays, and all plants [apart from aloes, and agaves which need good drainage] sit on them, so I can water the tray and let the plants soak up what they need.
Under the staging is where I store pots etc, because my greenhouse is in my courtyard, that part of it is always dark so that is storage only. Also, it is on concrete, so everything is in pots. I am slowly getting rid of all plastic though, and making my own wooden seed trays and deeper containers for growing everything in. The only thing that will be plastic soon is the large gravel trays that they all sit on. Hopefully, one it all changes to wooden - the soil dries out alot less as the wood holds moisture that can be taken up by the plant, I may not need the plastic at all. Hopfully.
I have those ikea stacking containers with the front opening bits, three of those - one for normal compost, one for bought in organic seed compost [so expensive] and one for home made leaf mould/seed compost. Which means plants can still sit on the top. You have to make as many horizontal surfaces as you can in a greenhouse. I also have two sawhorses with a long flat tray on top, for more plants. Again, these all to go at one point and to be changed for wooden alternatives.
I have saved up over the past few years and am hoping to get a builder to make a roof and front, using the two brick walls of our courtyard, and one wooden wall of our garden room, to make an orangery type greenhouse, which would be three times the size and mean we could have proper year round growing as we can then heat it. We can then also have space in the middle for sitting in properly. Work in progress! It will be on the space that used to be the old toilet, which now boasts a Belfast sink which I use to rinse down all the veg when it comes back from the allotment.
There is nothing like pottering in the greenhouse after a full day's spreadsheet wrangling/meetings with clients/colleagues. Clears my head.