You aren't going to significantly increase across ground the range by getting a better antenna or by putting out more power.
The primary thing that will get you further, assuming that is what you are talking about with simplex, is height above terrain.
If you have tall trees, the cheapest way to do that is with a slimjim antenna, homebrew or bought, and a chord over the top of a tall tree and pull the antenna up as high as you can get it.
A lot will depend on the surrounding terrain at your location. If you want to get on the other side of a hill or ridge, the antenna will have to be higher than the hill or ridge.
Even if the terrain is perfectly flat, you are still limited by the curvature of the earth and the higher you get the longer the signal will reach out. A typical hand held transceiver (HT ) to another HT is about +- 6 miles range over a flat treeless terrain like a large field of grass or over ocean. ( 6 feet high to 6 feet high over flat terrain ). Realistically in a suburban or forested environment it is half of that to 1/4 of that or less about 3 to 1.5 miles unless you get above the trees and building which block the signal but not as much as dirt.
If you were to get high enough to get the distance you want, and it is a long distance, then power and antenna gain in the horizontal will help. But first you have to get the height to get LOS
VHF / UHF is very much limited by line of sight ( LOS ). You have to get LOS before antenna gain or power will make a any significant difference.
If your antenna is at 20 feet, getting a new antenna isn't going to do much.
If your antenna is at 20 feet high, getting ANY antenna to 70 feet will be much better.