What near-future propulsion system(s) could be employed by my spaceships?

In a near future setting I am working on, humans have built space-habitats and have established colonies on celestial objects such as Luna. Their spaceships cannot go faster-than-light and have their fair share of other issues - yet are still the primary means of transport across the Solar System and are the result of constant improvement since the first space shuttle.

The void between these specks of life is populated by small-scale entrepreneurs, shipping cargo from a to b in trips that are measured in months to years. That is, thanks to cryogenics, for them only a few days pass, maybe a week.

They basically take on a cargo, plot the course and then wake up sporadically for maintenance, course-corrections, and so forth.

---

In a previous question I have been asking about plausible technological constraints that would favour text-interfaces over graphical ones. In this question, I want to focus on another aspect of my spaceships, namely their propulsion systems.

---

With some obvious exceptions, such as the cryo-sleep, I want most of the tech in this world to be current-day or plausible near-future extrapolations. E.g. the propulsion systems.

These ships traverse the voids of the Solar System on a regular basis. An excerpt from the schedule of a busy pilot might look like this (chronological order):

...
Deimos-Station        drop H2O cargo
                      pick up 20 ounces REDACTED (bribe T-Sony)
Hephaestus-Station    deliver REDACTED (payment for that Luna incident)
                      mixtape for Suul
                      pick up cheap and glittering stuff
SOL5-92-Jup92         drop off glitter stuff
                      visit Maja
...

¹

In order to get a feeling for the times involved in traveling these distances, I need hard numbers for things such as constant-/max-acceleration, fuel consumption, etc. of the propulsion system(s) in use by these spaceships.

---

Q: What near-future propulsion system(s) could be employed by my spaceships?

I am looking for answers with current-day technologies or plausible extrapolations of current-day technology.

An answer needs to address the following things:

• complexity of the whole system: The easier it is to repair/replace, the better
• achievable max-(constant-)acceleration: The smoother the better
• fuel consumption rates: Graphs would be amazing
• fuel efficiency: Space is a premium, the less fuel needed, the better
• fuel type: Being able to refuel between trips is great, having to replace whole sections of my engine after each trip is not

_{¹Station/staellites/asteroids (MINORS) are named after the convention STAR ORDER - ORDER_OF_MINOR - MINOR_DESIGNATION}