Something killed my baby bettas

I am not saying that plants are all bad, I just would not use live ones. There aren't a whole lot of places where you can pick up plants and not end up with snails or other pests. It certainly does not hurt anything to use fake ones.
Also, your tank will be fine but tubs make things a bit easier. You can still use a divider, most people make their own out of some platic craft sheet stuff. Plus, when you are dealing with only 4" of water, keeping the lid on helps you keep up humidity and helps to keep your temps from fluctuating. The humidity does need to be kept up a bit, since bettas are still labyrinth fish and need the humidity to help them grow their labyrinth organs.
P.S. I have bred bettas and gouramis in the past using these methods, I also know what works for me and what has worked for many others. Maybe it would be best for both of us not to assume that we know it all and meet somewhere in the middle. After all the point here is to try and help the OP.

I never assumed to know it all and wasn't disputing your suggestions. just rather pointing out the benefits of live plants. I've purchased quite a few plants from ebay and only one time did I get a unintentional hitchhiker. If plants are qt in a smaller seperate tank you can usually discover any unwanted occupants and ensure you only have plants going into your betta tank. you can keep the humidity high in a tank by using plastic wrap over the top of a tank.. I've had that work well. either way.. Joe can use which ever suggestions he thinks might work for him.

Agreed. Live plants do have great benefits. And, most hitchhiking pests can be taken care of by quarantine or a soak in chlorinated (untreated water). They are great for reducing amounts of CO2 in the water and are great for the nitrogen cycle. They can even be used for a partial food source in some cases (anacharis) or just to level the playing field to lower cannibalism and give all of the fry a fair chance. Floating plants are great for fish that need to hide out for a bit too, not just bettas.
For me, it is easier just to go with fake ones. I just don't have the time or space to quarantine plants or soak them, and the fish seem happy enough. They are also less maintenance and do not require pruning. I noticed that it would be impossible to siphon off dead plant matter while growing out tiny fry. I don't exactly have a green thumb when it comes to aquatic plants either..... I can breed fish all day long without trying but god forbid I try to keep one measly little bunch of anacharis alive for more than a few weeks. My java ball does ok though. Sorry Ladydragon.....I think I am just prejudice against aquatic plants.