New 3.5 gallon tank, stocking tips?

[Ems993]

Hello

I recently went to college and could only fit a 3.5 gallon tank on my desk. I had a betta in it, but she was very sick and ended up dying. I was wondering what kinds of fish would be recommended to start over? I'm not sure if the space was just too small for a betta or if she was sick when I got her (she never really swam around much) but I also never got a water heater (which i can totally get depending on recommendations) and I'm really just looking for some help to get healthy and happy fish.
Thank you so much to anyone who can help and I will gladly answer any questions if needed.

 

[NickAu]

3.5 gallon tank on my desk

Im afraid a 3.5 gallon tank is too small for anything but some shrimp or a Betta.

What did your fish die from?
What are your water parameters, Is the water hard or soft?

 

[seangee]

Does your tank have a filter?