These are just a start and there are a lot of other options.

There are miniature scabiosas, garden phlox, quite a few rock garden plants about that size and smaller, miniature monardas, and sedums all of which can be found as seeds, all around that size. Also miniature shasta daisies and hardy mums. All which can be grown from seed. What I have seen of Little Goldstar's big sister, Goldstrum which is also available from seed is that many of her seedlings do not get much bigger than Goldstar. There are quite a variety of coreopsis that start pretty easily from seed. Also dwarf poppies, and shortlived but reseeding perennials like gallardias and reseeding annuals like calendula. Some of the reseeders become established and are then as good as perennials, calendula and gallardia especially. Don't forget the hardy dianthus, maybe not as dramatic as true carnations, but lovely and mostly fragrant, except for the biennial ones. Some of the alliums both ornamental and edible will also fit, chives and garlic chives come to mind, but dead head because they seed so massively that they can easily become invasive.

I believe they also have dwarf echinacea now and in some interesting color variations. Once established a bed of echinacea has quite an appeal to it. And I believe there are also dwarf balloon flowers now. Both of them are long lived and hardy once established without being invasive and become old friends. Much the same goes for the columbines though they tend to be shorter lived but often reseed themselves to make up for it.

The longer lived of the perennials tend not to flower until the second year. Those that come into bloom early say late in the first year tend not to last so long, but very often will self sow, at times vigorously.

Most of these can be started much like you start tomatoes or peppers inside, or better like cabbage and broccoli starts, since most hardy perennials often actually germinate better in cooler temps. They can also be started outside, but generally then require a second year to come into blooming instead of cheating with the earlier inside starts.

BTW most of the seed catalogs are not really that much off base, provided you handle the growing conditions properly, and make allowances for their sales pitches.

Most of what I mentioned above, once started and properly spaced need little more than attention to keep from drying out the first year. Plant the seedlings so that they do not crowd or fill in their allotted space for about three years and fill the open spots in between with annuals. Mulch with coca bark or wood chips. If you mulch with stone or crushed rock, you will almost certainly live to regret it, and you will be stuck with it anyway. Removing rock mulch is a very difficult task.

After that plan to divide and reset the true perennials about every three years or whenever they get crowded. Also plan to thin volunteer seedlings very early so that they do not over run everything, and dead head all developing seed heads before they ripen except a few strategic ones on the self sowing types, or you will end up with a jungle that will seem more weedy than pretty. Dead heading spent blossoms immediately as they wilt will often encourage some of the shyer bloomers to rebloom. Many of the blossoms are actually edible, too, but be very careful some of our prettiest flowers are very toxic.

You are apparently looking for sizes that do not need to cut back to stay in bounds. As far as height goes you have a lot of choices. Probably best to stay away from the ground cover types, since they can take over and in some cases actually be close to impossible to eradicate.