You can buy an original R4 on Ebay or AliExpress if you really need / want one (they're the no label cart). I personally don't recommend them when you can get something else like an DSONE or Acekard 2, since you're gonna be using it on a NDS Lite.
Using an original R4, the only advantage you'll have is WoodR4 compatibility. Meaning most games can be played without patches.
The advantage with a DSONE, is it has a CPU physically in the cart, so it has a real-time cheat menu. Very good game compatibility as well.
AceKard 2 is a decent choice as well. It doesn't have a CPU physically in the cart like a DSONE, but the menu is pretty and functional like WoodR4.
And the R4 clones... They work, but they're not a great experience compared to the DSONE and AceKard 2. A clone like the r4isdhc.com is okay since it has a real-time cheat menu similar to the DSONE (although not the same experience) and has WoodR4 (albeit a very outdated version). The only problem with the r4isdhc.com R4 clones, is the time bomb. The flashcart will stop working after a certain date due to the kernel. This can be bypassed however, by using YSMenu.
I won't mention the R4i Gold 3DS Plus because they're not available on the market to buy.
tl;dr Buy a DSONE. If you can't, buy an AceKard 2. If you can't.... buy an R4i SDHC Gold Pro (r4isdhc.com version). If you really can't... I don't know what else to tell you.