Everyone is different so there's no telling how you'll feel. You may be fine to shower without a bench or chair, or you may need one. I didn't need one, but many others do. I didn't take a shower until just over two weeks due to my pain ball, but you'll likely take one much sooner.
I was given a couple of "showers" while at the hospital, but they covered my leg with a plastic thingy and I sat in a chair. It wasn't a true shower, more like a sponge shower and my hair was washed. But when I took actual showers at home I never used any aids. I just walked in and stood for it.
Maybe you could order one just before your surgery, and if you don't end up needing it, send it back. Or, if you have any of those plastic outdoor chairs, and if it'll fit in your shower, just use one of those.
Also, if you do sit at first a hand held shower head is helpful. If you don't already have one you can get them at the chain hardware stores really inexpensively and toss it when you no longer need it.
I also bought some of those disposable washcloths to use until I was able to shower and washed my hair at the sink for a while. The disposable washcloths actually work well not as well as a shower but well enough.