One metre of lightweight multi-layer thermal insulation will do the trick.

By this point the heat generated by your crew will become a problem to be be disposed of, even though it is extremely cold outside.

The bigger questions are:

How big a crew/colony will you send?
500 individuals is an often-quoted minimum for genetic diversity, although this could be improved by sending a large cargo of genetic material in the form of ova and sperm from individuals not on board and ensuring that for the first few generations at least, that 50% of new births were from such IV material rather than from the population at large - or 100% of births were from one colonist and one donor

Where will you be going?

To date we have no expectation that a habitable planet exists around any of the Centauri stars. Of course, if you are assuming that we will simply build a habitat there, then you are assuming truly science-fiction levels of engineering. It would be much easier to build such habitats in our own system in resonant orbits with Earth

Ultimately, we would perhaps be able to build a hollowed-out asteroid and use that as the colony ship itself, with a stable population of 10,000 or so and a journey time of many generations. Of course, one might ponder why such a ship need ever bother to stop at a star system, but perhaps it would need top refuel and replenish lost volatiles etc., but it would be a good seed ship. The human race, devoting its entire resources to the project, could probably build one such ship each century.

Each star that was visited that had a habitable world could have a colony dropped off, taking ~100 years to be established, then 1000 years to grow until it in turn could begin manufacturing seedships.

Travelling at 1% C, such a ship could cross our galaxy in 100,000 years. With pauses for stops, say 1 million years. So in one or two million years a wave of human colonisation could occupy essentially every single habitable world in our galaxy (what a horrible thought!).

Of course, the above makes major assumptions about technology!