How much can you get down the length of the garden before you need to bend it?
There are plenty of completed models out there for the EFHW, for example, and you could grab those and the software used and simply change the wire orientation....BUT remember with a multi-band antenna, the [pattern changes per band, as the effective height above ground changes relative to wavelength.
A good place to start reading is here.....but personally, for the cost of the 20m of wire you're talking about, I'd grab a mate you can get some signal reports off on your favorite band, where you're not always a 59, put the new one up, and try it again...that's what I did.
https://www.qsl.net/kk4obi/EFHW%20Straight.html
https://forums.qrz.com/index.php?threads/efhw-antennas-radiation-patterns-vs-frequency.692671/
I appreciate a disability is going to make this more of a PITA than for some of us, but that's why we have mates!
