Any 1997 - 1998 T5 M4.4 ECU will be your best bet
I used one from a scrapped S70 T5, socketed the ECU and bought an Ostrich for a 1/4 $ of the TT units
With these you can tune via USB on the cheap, or invest a bit more and have more functionality than even the hugely overpriced TurboTuner ECUs
https://ozvolvo.org/discussion/4417/motronic-m4-3-to-m4-4-socketed-ecus-and-ostrich-2-0-what-it-all-means-and-why-bother/p1
I haven't added any more info in the past few months, Ill be doing a BIG update in about 7 weeks