Most objects that grow to less than 8/10 ft are called a bush rather than a tree, and many such bushes are available. Though there are some dwarfed trees that grow very slowly, mostly conifers like you mention. But most dwarfed conifers do carry on growing, just very slowly, and at 20 yrs will be higher, possibly a lot higher, than their "height at 10 yrs" or whatever is quoted. Buy your dwarfed conifer from a reputable supplier or you might get a surprise. I bought a dwarfed Arbutus unedo, an evergreen rather than a conifer, which was called an 8-10 ft tree on its label. It reached that after about 5 years and I have been pruning it hard ever since, often by 2 feet a year. Some can be very small: I had a dwarfed spruce which never got higher than about 50cm before a drought killed it off after about 10 years. I had a dwarfed Scots pine which grew to about 1m20 in 10 years before I had to move it due to building works and it didn't survive. I have a variegated Korean pine (not the commonly seen K fir) which is due to grow to 30ft or so, but will probably take a century to get there; since it is now about 15 it is still only about 1m50...

Another option is to get a weeping form which has a pre-defined height. For example, I have a weeping Atlas cedar and a weeping flowering apple (ie one that is no use for its fruit, not even for crab apple jelly) which are both just the same height as when I bought them. I didn't understand this properly when I got the cedar, if I had I wouldn't have got one that was just 3ft tall...

Another option is called pruning, as is commonly adopted for hedges, for example, but trees of suitable species can also be controlled by the pruning method called pollarding which keeps them to a defined height by routinely heavily pruning them each year. There are also in-the-ground bonsai techniques, as you can see at Wisley, though that is very hard work.