There are many dwarf rhododendrons that will be under 4 feet in 10 years, but none that stop growing at that point. Rhododendron 'Crete' for example, is usually listed as a dwarf, but my oldest one is now around 7 feet tall after 25 years. The width can be controlled by pruning, but the danger is winding up with an odd looking narrow specimen with lots of bare lower branches. Some rhododendrons grow in a more upright manner than others, but most and especially dwarf types naturally assume a mushroom shape as they grow. This This is usually considered a desirable trait so narrow forms are scarce in the market.

Any dwarf rhododendrons you can recomend?

Most of the yak hybrids will stay quite compact, around 4'x4' after a good number of years. These also tend to be quite sun tolerant and relatively pest free afa rhodies go. But there are LOTS of dwarf rhododendrons........R. impeditum will stay quite small. Also look at 'Cream Crest', 'Ginny Gee', 'Patty Bee', 'Wee Bee', 'Shamrock', 'Hardizer's Beauty', 'Ptarmigan'.

Note the form on most of these is low and mounded to somewhat spreading - few will exhibit a very narrow growth habit.

It would be very helpful to know your location. Dwarf rhodendrons can vary considerably in hardiness. I agree with gardengal48 that yakushimanum hybrids as well as the straight species are good choices and most are very hardy. gardengal48's non-yak supplemental list contains some varieties not nearly as hardy. Wee Bee and Ptarmigan, for example, are rated only to 0 or slightly below.

Here's how to add zone and location info so it shows up like GG48's and mine, automatically next to your name each time you post. It is helpful in getting useful recommendations.

Go to Your Houzz in the upper right of every page, click Edit Profile, and on the left side click advanced settings. Well down the advanced settings page is a blank labeled Climate Zone for Garden Forums along with a link to find your zone.

If you add info on your country (if not US) or state/province or the nearest large city you will get even better information since zone only relates to average coldest winter temperatures.

Then return to the top of the page and click Done Editing.