Not rosy reds cause they get too big as well. Well actualy they only get to around 4" but they need mroe swimming space.
Options are mosquito fish (a trio or 2 males, 3 females). This is heternadria formosa I am reffering to which is small grows to just about one quarter of an inch to half an inch in size. Because they are absolutely tiny, you can keep many mroe than just five but they breed like guppies so leaving room for fry is wise. Livebearers. Don't mix with anything aggressive or much larger as they'll get eaten or killed. A breeding, species tank is best.
There's also gambusia afinnis the western mosquito fish. These are a little more nippy but would be ok with their own kind. They get to 1.5". Again, a livebearer.
A bitterling would work as well. They get to 3.5". Note that there are several species. Some are schooling fish so avoid those as they'll want to be in a group which there is no room for in a 10 gallon.
Orange-spotted sunfish get to 4" but I would just keep the one in a 10 gallon alone as they are territorial and do best in a species tank (in a 10 gallon you can't realy keep many comfortably so stick to the one fish). There is also the pygmy sunfish which is lovely, stays very small at 1.25" and would do great ina little species tank.
Also, about keeping goldfish in this tank. There are a few varieties that could actualy work - for example, a single bubble-eye or a pearlscale (one of the ping-pong ball type ones). That's because they stay smaller than most goldfish (inbreeding is to blame for that). However, they still enjoy the company of others of their own kind and are still major poop-machines. As such, I personaly wouldn't do this. I just wanted to point out that it is actualy possible.
IMO, go for some mosquito fish and white clouds. If your tank has a strong current and plenty of river-type, rounded rocks, you could consider a hillstream loach as well but you are best off skipping it if you cannot meat its requirements.
Alternatively, get some pygmy sunfish. Very cute and very interesting. Don't over-crowd them though as they need to be able to establish territories. Planting the tank ehavily and putting in rockwork and things to divide up the tank will enable you to keep more.
There are also quite a few borderline tropicals that would do well in 70 deg F water - golden dwarf barbs are one of my favourites and, as they are small, a school of them would be nice in a 10 gallon. They get to just over 1".
In fact. most of the hardier barbs can be kept in 70 deg F water. Checker and stoliczka's barbs can live in water as low as 66 deg F. However, at elast 70 is best and it should be constant.
There's also quite a few killifish that do fine in lower temps but, realy, I wouldn't risk anything lower than 69 deg F and it should be steady.
Fluctuating temperatures would not be good for any borderline tropical fish. Well actualy fluctuations aren't good for any fish but it's worse for tropicals in this case.