There are some newer ones coming out real cheap that are based on plastics. The end of the bristles is very fine and very soft, but the main part lays paint down. Run your hand over the end, if it feels soft and is white, they're probably the kind I mean.
I paid about £4 for one from toolstation.com and I absolutely love it.
In terms of getting a good finish, you need to get artistic.
Firstly, do your cutting in and roller work at the same time. Secondly, when you cut in with the brush, run most of the paint off it building up the really transparent areas and then 'dust' the brush lines. I mean, when there's next to no paint left on it, sweep over over the brushed area to smooth it into the roller area. For a reference, download "bob ross, the joy of painting" and listen to what he says about creating mirrors in water.
Personally, if I'm doing a room now, I have the tray in my left arm and a big brush and roller in that. I brush the joins, the immediately roller the big areas, so the two dry together and have the same paint tin and same conditions as they go.
I've spent so long taping seams and then had them come out all nasty. The easiest way to is use an emulsion on the wood and an emulsion on the walls. Brush the contours of the wood, then rollers the walls before the brush work has dried.
I've had one of those Titan 440 airless sprayers. They do not help at all for domestic work. They'll empty a 10l tub of paint in minutes, the finish won't look very good and so on. They're designed for doing a whole floor of flats per days. The gun is either on or off, the flow rate isn't controllable in that sense. And that's over £1k's worth of painting gear. I know how to use spray guns, have respirators, know about composites, catalyst and have 5l containers of the solvent in paint stripper. Those commercial airless guns are too fierce.
I am considering trying the Wagner paint crew (115) models, the kind where the paint is in a hopper on a cart. But even the entry level airless gear is WAAAAY too much for domestic work, unless you have a house that is literally empty and waiting for the finishing work (sockets, switches, window fames etc).
Emulsion also has very nice self leveling. You can brush it, it will look all streaky, then it'll dry smooth. Gloss takes FOREVER to fully go off, it yellows, even the none yellowings, it needs a messy clean up and it's not at all hard wearing or chemically resistant. If you want those things, use urethane. Gloss works by oxidizing in the air, but it takes a stupid amount of time to fully cure. Weeks or months. Urethane dries quickly, doesn't yellow and is really resistant. Epoxy is evil good (the stuff they use on warehouse floors), but costs a ton and the whole batch goes off once it's mixed, usually quite quickly; so you need to move fast and need that level of resistance.
I swear, I've repainted walls, boards, rails and fitting so many times I've lost count.
Use emulsion. Brush it, roller it, dust the brush lines. Forget the tape and airless gear.
This is the precise brush I'm using
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