it's tricky, stuff like psp's vintage warmer and it's mix 2, as well as tape/valve sims can give you the warmth but it has to be done right.
there are some excellent hardware compressors by the big names such as api, neve, avalon, ssl, massenberg, etc that can be not as expensive as you would think, at least some of their versions. plus check for used ones on ebay, craigslist or from store sites as well as discounted ones used for demonstration might be the way to go.
another option is a summing box, to possibly get that analogue imperfection aka warmth (not always but..).