Both my boys loved thier Amby hammock. Imran stayed in it for his day sleeps until after his first birthday so a shorter one wouldn't have been such good value for us.
I wouldn't bother making plastic backed sheets since in summer they would reduce airflow and might be a bit sweaty. The matress isn't very thick and nor is the cover. I found that if they needed wash in summer I could wash them in the morning and go out for a few hours and they would be dry when I got back. In winter they would dry before bed timeon a sunny day with a bit of a breeze.
I bought sheets but it would have been easy to make them.
I usually put the boys down wrapped and if the needed a bit of extra warmth I used baby wraps as blankets.
When Imran was very small I used one of those back snuggler things (with a roll on each side and a bit of fabric between to stop them from rolling - in baby shops) to keep him centered.
Yasin was about 3 months old when we got it and took about a week before he decided that he loved it.
You can rent them so if you wanted to try before you buy that's a great option