if you invest in changing the return air filter rack (the whole
grill where you change the filter) you can buy a media filter
grill. 4-5" filter fits into this grill.
once system duct/return is sealed...the media filter filters
a lot more particulte matter than 1" pleated media filter
and is less restrictive. I recommend media filters to
everyone who has sealed duct/return stystem.

there is also a media filter that fits into the
existing return. more expensive than the one
that requires the change of r/a filter grill.

so do the math.

both filters are changed 2 times a year.
so you re-coup some of the cost.

electrostatic filters are crap.
uv lights aren't necessary if stuff isn't entering duct return
they are great at killing mold spores. but is system doesn't
have leaks/condensation & food source..they aren't needed.
also bulbs have to be changed every couple of years.

best of luck.