Leopard gecko loose substrate options?

[Lizrd_boy]

Hi there! So, once Lenetta is done laying for the year I want to move her into an upgraded 30 gallon enclosure. While I'm at it I want to change her substrate from cage carpet to something that will give her a little more opportunities to dig and have a more naturalistic setup. Not a full bioactive, not yet at least, I can't handle that right now, but something to give me some more things to look after in the geckos tank.

I was thinking I would go for a DHP for the heater, since I've heard they heat geckos very efficiently, despite being heat from above. How would you recommend I control it?

I also have an 18" flourescent fixture I was thinking I'd use with a UVB/UVA bulb for both the gecko and the plants (I'm not entirely sure this is the correct type of UV for plants so I'd appreciate any insight on that). I'd switch the gecko from calcium with D3 to without it so she doesn't get too much.

As far as substrate, I was thinking I'd use a sand/topsoil mix. Does anyone have a better idea or anything? Also, How would I go about disinfecting the stuff first? I'm gonna be using regular lay sand and organic topsoil I'd buy from some hardware store. Not sure exactly where yet.

For plants, what plants are safe and good looking, and relatively easy to keep alive in a geckos tank?

Any other advice is greatly appreciated, I have not had experience with anything this elaborate before but I think Lenetta would enjoy the extra space and opportunities so I want to give her that.