[beautiful Betta]

White or gold, cloud minnows are a small fish that you could get away with without a heater. Although they are a shoaling fish so you would want at least two. You would need to have a 2 gallon for that minimum, they are fairly easy to feed only needing a very small amount of flake food. They only grow to around 4 cm max. I would recommend a small filter. But with regular water changes and the use of prime you may be alright without a filter.
They also come in a longer fin types as well.

However if you really don't want maintenance in a weekly form at least, then perhaps you should look at a glass floating fish that is just for decoration, and needs no maintenance at all.

 

[beautiful Betta]

couldn't find glass floating fish, but if you just want something bright in a bowl of water, why don't you get these no maintenance required.
[http://www.ebay.com.au/itm/Aquarium...095334?pt=AU_Pet_Supplies&hash=item2a2be59fa6

You could use a different one every week, or all of them, overstocking wouldn't be a issue, I promise. lol:-D

 

[bettacrazygirl86]

The floating fish idea is cute. My mom got me a little tank that you can actually plug in and it has a built in filter that makes the little plastic fish swim.

Anyway. If you really want another betta, I highly suggest upgrading. I have my betta in a 10 gallon and I do a water change every weekend. Parameters are fine, fish are perfectly healthy, and everyone's happy. So if you can get a bigger tank, something 5 gallons or bigger, you should be alright.

What is the temperature of water at room temperature? I've known some people in Australia to get away with no heater because of the temperatures over there. You will probably need one eventually, when it gets colder (autumn and winter), but for the spring and summer, you probably won't really need one other than to keep temperatures steady. Depends on your water temperature. Bettas like 76 to 82 degrees F.

There are plenty of 5 gallon tanks that don't take up a lot of space. I have a MiniBow that fits on my nightstand beside my bed. The filter's a little pushy, but my betta doesn't seem to mind it very much.

 

[beautiful Betta]

I am in Australia and I don't think there are many places here that would be able to support a betta properly in the winter time temperature wise. I am in QLD which is one of the warmer states and we are now in autumn will be winter soon and already the heater is coming on, the house temperature is dropping down to about 69F now. The only real places that a heater wouldn't be needed is the northern area's and states. area's such as Cairns (Great barrier reef area).