I’ve been using a Suunto Vector altimeter watch for about ten years. Easy to set, easy to read during flight, large numbers, rugged. There’s a lightly used one one EBay now for just $31. https://www.ebay.com/itm/Suunto-Vector-Watch-Compass-Borometer-Altimeter-Black/292758935922?epid=1210529356&hash=item4429cad972:g:C6AAAOSw3Ypbt-YV