and would appreciate some advice and/or tips on holding altitude accurately
Start with the basics, a correct scan LAI; Lookout (wing tip to wing tip) pause in the middle, and check the Attitude (pitch and wings level) then briefly check the Instruments (Altimeter and Ball). If you spot an error adjust the attitude and balance before continuing the scan.
It takes quite a while to regain altitude which tells you that it also takes quite a while to deviate from it, so you are not picking it up and acting on it soon enough.