If you can't find ottos, another option could be rubberlip plecos or pitbull plecos. Since you are already adding driftwood for the current pleco to feed on, the rubberlips would also be OK in your tank.
Like Mr Limpet said, nerite snails may try to escape from a lidless tank, but you could give them a try. I have one that's behaved, but I also have a full hood on my tank.
My amano shrimp will stick to the side of the tank and eat algae off of it, but they aren't going to make any significant dent in it.
You may also want to think about decreasing your lighting to combat the algae if it's growing too quickly. I've just recently decreased the lighting on my tanks from 10 to 9 hours to slow algae growth to a crawl, but still have some for the algae eaters in my tanks.