From what I've found, most 19" LCD monitors seem to use 1280x1024 which is 5:4 rather than 4:3. Granted, 1280x1024 was a somewhat common resolution (certainly more common than 1280x960 for some reason) and most programs/games from the Win98/XP era support that resolution. But if you are running other lower 4:3 resolutions (eg 640x480, 800x600, etc) things may look janky/skinny/bad when scaled to 1280x1024. Also I've found that most LCD monitors of that era tend to have shoddy internal scalers, which doesn't help.
There were some higher end LCD monitors that ran 1600x1200 (typically they were 20" monitors). That is of course a 4:3 aspect ratio, but will be a fair bit harder to find than a 19" LCD. Another option is to find a 24" widescreen monitor (eg 1920x1200) which supports pixel perfect 1600x1200 (black bars on left & right, no stretching). From your post, I'm not sure if this is what you're already doing...
In regards to you question about loosing anything... I find that most XP era games look fine on 4:3 even if they support widescreen. And many of the newer XP era games that are BETTER on widescreen... tend to work fine in Windows 10 on modern hardware.